I made the following statement in my paper earlier today, entitled: Martin Luther's Positive Statements on the Christian Status of the Catholic Church as a Theological Worldview: Documentation:
Another relevant factor to take into consideration is Luther's ravings when he was an old, embittered, sick man (disgusted even with most Protestants, including his own party, let alone Catholics): often regarded as from 1543 till his death in 1546. Many -- if not most -- Luther scholars think they should be taken with a large grain of salt: certainly not literally all down the line. Some of these rantings are blatantly anti-Catholic in nature; other famous pontifications from this period are his jeremiads against the "Sacramentarians" (Protestants who denied the Real Presence in the Eucharist) and the Jews.
The context had to do with Luther's view of the Catholic Church: whether it still retained Christianity or could be regarded as Christian in some sense. I documented his affirmative views in that paper, but I also noted that he said many negative things, and that as an old man his rhetoric was so ratcheted-up that it must be interpreted a bit differently, taking his illness and frustrations, etc. into consideration.
Now, that rankled and distressed James Swan, an anti-Catholic Reformed Protestant polemicist, to such an extent that he felt compelled to rail about it on his site, Boors All: as usual, neither naming me nor linking to the paper where I stated this, so that folks could examine context (even though he quotes me directly).
All of this is quite ironic and ridiculous, of course, since Swan rants constantly about how Catholic apologists care nothing about context. Moreover, if I dare to show up on his site to give the link to the latest paper of mine that he is obsessed with as of late, and dare to present another side, he deletes everything I put up. Can't be too careful these days, in preserving cynical propaganda against criticism from those wascally wicked "Romanists"!! Here is what he wrote today:
Oh no with Luther, if he's saying something Romanists don't like which disagrees with their preconceived historical revisionism, Luther isn't "developing." Rather, he was such an erratic thinker that he contradicted himself month to month, and... to make it worse, he was "an old, embittered, sick man" so anything he said later in his life can't be trusted. . . .
Luther did not consider the defenders of the papacy to be Christians, and even in 1520, in a restrained way he's saying the same thing he did 20 years later when he was "an old, embittered, sick man."
First of all, I didn't say that we should entirely discount "anything" Luther wrote when he was old, sick, and embittered. I simply stated that it was "another relevant factor" and that (Protestant) Luther scholars "think they should be taken with a large grain of salt: certainly not literally all down the line." Big wow! This is, unfortunately, classic Swan tactics: distort what the opponent says; don't cite it in context; don't provide a link for the same ends; don't allow the person to respond on your site; then proceed to tear down the straw man that isn't even the person's actual opinion, in an effort to defame and belittle. I never claimed that later Luther statements were to be completely disregarded or dismissed. But for Swan (given to myths and fairy-tales, above all, whenever the detested, despised "Romanists" are involved), somehow I did do that.
I shall now proceed to back up everything I stated from Protestant biographers, and even from John Calvin and Heinrich Bullinger: contemporaries, fellow "reformers" and acquaintances of Luther (if only by letter).
Roland H. Bainton
[author of Here I Stand: A Life of Martin Luther (New York: Mentor Books, 1950): without question the most well-known and probably most renowned -- certainly most influential -- Luther biography in English; citations from the Internet Archive version, that can easily be searched by word; excerpts from chapter 22: "The Measure of the Man"]
The last sixteen years of Luther's life, from the Augsburg Confession in 1530 to his death in 1546, are commonly treated more cursorily by biographers than the earlier period, if indeed they are not omitted altogether. There is a measure of justification for this comparative neglect because the last quarter of Luther's life was neither determinative for his ideas nor crucial for his achievements. . . .
. . . the conflicts and the labors of the dramatic years had impaired his health and made him prematurely an irascible old man, petulant, peevish, unrestrained, and at times positively coarse. This is no doubt another reason why biographers prefer to be brief in dealing with this period. There are several incidents over which one would rather draw the veil, but precisely because they are so often exploited to his discredit they are not to be left unrecorded. The most notorious was his attitude toward the bigamy of the landgrave, Philip of Hesse. . . . Luther's solution of the problem can be called only a pitiable subterfuge.
. . . The second development of those later years was a hardening toward sectaries, notably the Anabaptists.
[Bainton goes on to detail how Luther and Melanchthon adopted the view of capital punishment against them]
. . . Another dissenting group to attract Luther's concern was the Jews.
[Bainton analyzes -- with obvious disapproval, as in all these cases -- the horrible and famous statements that Luther made against them, stating, "One could wish that Luther had died before ever this tract was written."]
. . . The third group toward whom Luther became more bitter was the papists. His railing against the pope became perhaps the more vituperative because there was so little else that could be done. Another public appearance such as that at Worms, where an ampler confession could be made, was denied Luther, and the martyrdom which came to others also passed him by. He compensated by hurling vitriol Toward the very end of his life he issued an illustrated tract with outrageously vulgar cartoons. In all of this he was utterly unrestrained.
. . . However much the superb defiance of the earlier days might degenerate into the peevishness of one racked by disease, labor, and discouragement, yet a case of genuine need would always restore his sense of proportion and bring him into the breach. . . . Luther's later years are, however, by no means to be written off as the sputterings of a dying flame. If in his polemical tracts he was at times savage and coarse, in the works which constitute the real marrow of his life's endeavor he grew constantly in maturity and artistic creativity.
There you have it, folks. I outrageously (?) describe Luther as "an old, embittered, sick man . . . disgusted . . .." Two of those words are undeniable ("old" and "sick"); so the only "controversial" things I said was that he was "embittered" and "disgusted" (with various shortcomings among Protestants and all of his other concerns).
Bainton, his leading biographer (and great admirer) describes him, on the other hand, as "prematurely an irascible old man, petulant, peevish, unrestrained, and at times positively coarse. . . . more bitter . . . [producer of] outrageously vulgar cartoons . . . utterly unrestrained. . . . the peevishness of one racked by disease, labor, and discouragement . . ."
I stated that his "last years" were roughly from 1543-1546. Bainton dates them from 1530 on: 13 years earlier than my given dates. He even notes how historians generally greatly underemphasize the last 16 years of Luther's life. Thus, for Bainton (and Church historians generally), this is a far bigger factor in Luther analysis than in my view. Yet I am supposedly so "anti-Luther" and they are not.
Which is worse? I get trashed as a mere partisan of "Romanism" who cares nothing about historical fact, because I supposedly despise Luther (I don't: I admire him in many ways but am also a strong critic of his theological errors and whoppers about the Catholic Church and catholics: none of it entailing hatred or calumny), while Bainton gets a pass for stating far worse than I did? That is James Swan's Alice-in-Wonderland world, where facts are irrelevant and logic is a joke, and Catholics always wrong, wherever they disagree with Protestants: about anything whatever!
[author of Martin Luther: The Preservation of the Church: 1532-1546 (Minneapolis: Fortress Press, 1993, from the 1987 German original; translated by James L. Schaaf) ]
. . . recent presentations have treated the last two decades of his life more or less cursorily . . .
It is well known that the personality of the old Luther displayed great tensions, both in deed and thought, His shortness and rudeness with his friends, although perhaps explainable, continually caused offense. In the many tasks that he had to perform, it was unavoidable that he also repeatedly made serious errors both ion practice and in theory. (Foreword, pp. xi-xii)
In February  he was engaged in writing Against the Roman Papacy, an Institution of the Devil . . . It was written in an extremely vehement manner, full of crude statements and vulgar expressions. He was probably unable, because of his declining abilities, to organize it in as well-balanced a manner as he planned. To this extent, it is not one of Luther's best works, but its offensiveness and formalistic weaknesses need not divert us from seeing that once again he was dealing with essential matters in his conflict with the papacy. (p. 359)
Although the manifestation of Christianity in the papacy was a pollution to Luther -- theologically, juridically, ecclesiastically, and politically -- his reaction was still inappropriate, for, conditioned in his anger and eschatological bias, he could scarcely see any positive alternative in the controversy that concerned him until his end. (p. 367)
Mark U. Edwards, Jr.
[author of Luther's Last Battles: Politics and Polemics, 1531-1546 (Ithaca, New York, and London: Cornell University Press, 1983) ]
It becomes difficult to escape the impression that Against Hanswurst  represented an escalation in the coarseness and abusiveness of the controversy . . .Heinrich Bullinger of Zurich [fellow Protestant "reformer"] . . . did characterize it in a later letter to Bucer [another "reformer"] as 'unbecoming, completely immodest, entirely scurrilous, and frivolous,' but his evaluation remained private. (p. 154)
Here is an excerpt from Luther's work, that Edwards cites on pp. 150-151:
You are both the real Hanswursts, bumpkins, louts, and boors . . . Both of you, father and son, are incorrigible, honorless, perjured rogues . . . But suppose what you will, so do it in your pants and hang it around your neck and make a sausage of it for yourself and gobble it down, you gross asses and sows!
The last major polemic of Luther's life [Against the Papacy at Rome, Founded by the Devil (March 1545) ] . . . was intended to inform Protestants of the true horror of the papal antichrist and to discredit the council convened at Trent . . . Without question it is the most intentionally violent and vulgar writing to come from Luther's pen. (p. 163)
The Introduction for this hideous tract, in Luther's Works, the 55-volume American edition, describes it as "the most bitter of Luther's polemic writings" (LW, 41, 259-290)
During his later years Luther's polemic never flagged. His last book, Against the Papacy of Rome, founded by the Devil, surpassed Cicero and the humanists and all that had ever been known in the virulence of its invective . . . Of course such lack of restraint largely defeated its own ends. The Swiss Reformer Bullinger called it "amazingly violent," and a book than which he "had never read anything more savage or imprudent." Our judgment of it must be tempered by the consideration that Luther suffered in his last years from a nervous malady and from other painful diseases, due partly to overwork and lack of exercise, partly to the quantities of alcohol he imbibed, though he never became intoxicated.
(Reformation in Europe, Book I of a two-volume edition of The Age of Reformation, New York: Collier Books, 1962; originally 1920, 102)
Writing to Luther's right hand man Philip Melanchthon, Calvin stated:
Your Pericles [Luther] allows himself to be carried beyond all due bounds with his love of thunder . . .
But, you will say, his disposition is vehement, and his impetuosity is ungovernable; -- as if that very vehemence did not break forth with all the greater violence when all shew themselves alike indulgent to him, and allow him to have his way, unquestioned. If this specimen of overbearing tyranny has sprung forth already as the early blossom in the springtide of a reviving Church, what must we expect in a short time, when affairs have fallen into a far worse condition?
(28 June 1545; Letter CXXXVI in Selected Works of John Calvin: Tracts and Letters, edited by Henry Beveridge and Jules Bonnet, Volume 4: Letters, Part 1: 1528-1545, translated by David Constable, Philadelphia: Presbyterian Board of Publication, 1858; reprinted by Baker Book House [Grand Rapids, Michigan], 1983, 466-467)
He was even more critical in a letter to Bullinger (the "reformers" had a knack of griping about each other in such letters):
I hear that Luther has at length broken forth in fierce invective, not so much against you as against the whole of us [referring to Luther's Short Confession Concerning the Supper] . . .
But while he is endued with rare and excellent virtues, he labours at the same time under serious faults. Would that he had rather studied to curb this restless, uneasy temperament which is so apt to boil over in every direction. I wish, moreover, that he had always bestowed the fruits of that vehemence of natural temperament upon the enemies of the truth, and that he had not flashed his lightning sometimes also upon the servants of the Lord. Would that he had been more observant and careful in the acknowledgment of his own vices. Flatterers have done him much mischief, since he is naturally too prone to be over-indulgent to himself. It is our part, however, so to reprove whatsoever evil qualities may beset him, as that we may make some allowance for him at the same time on the score of these remarkable endowments with which he has been gifted.
(25 November 1544; Letter CXXII, ibid., 432-433)
See also my related 2004 paper, Biographer Roland Bainton and Other Protestant Historians On "Controversial" Issues Concerning Martin Luther, and lots more Luther analyses on my Martin Luther web page.