Ruth Gay has this about him on p. 84:
The model of the court Jew was Josel of Rosheim. Although he was born in Alsace, Josel's powers of persuasion were so efficacious that he was importuned for help by Jewish communities in places as distant as Bohemia, Saxony, Silesia, and Hungary. Born Joseph Ben Gershom at the end of the fifteenth century (ca. 1478), he lost his father at the early age of six. The family had paid bloody dues to the superstitions of the time: three of Josel's uncles were condemned to a grisly execution in 1470 following a blood libel in a celebrated case in Endingen. We can only conjecture about the effect of this somber background, but we know that Josel must have had a remarkable presence, because he was early prevailed upon to intercede for Jewish communities in trouble. In 1520, at the coronation of Charles V, Josel managed to procure a letter of protection from the new emperor for the Jews in German lands. Accorded honorary titles by grateful Jewish communites, he became their single most important spokesman against the recurrent blood libels, the ever more violent denunciations of Luther, and the calumnities that regularly threatened the continuity of Jewish settlements.Ruth Gay also presents information about the lives of two, not as illustrious court Jews, Lippold and Joseph Suesskind. We will quote her regarding Lippold and leave you to look up Suesskind's story.
During the sixteenth century a rather more indirect form of attack--staged disputations between learned Christians and Jews--was at the height of its popularity...
While Josel earned his living as a money-changer, his commercial activities fade against his lifelong service as an intercessor. He was also, as we have seen, an intellectual representative of Jewish thought and belief to the Christian world as well as a scholar securely within the Jewish tradition. He wrote philosophical works on ethics and even an autobiography shortly before his death in 1554. Both in his influence and in the use of his powers, this remarkable man, who won such favor with Charles V that he and his family were given permission to travel and settle where ever they chose, was unique among court Jews.
Unfortunately, Josel's memory neither improved the character nor protected the life of the court Jew Lippold, the rapacious accomplice of the elector Joachim II of Brandenburg, who came into prominence at the time of Josel's death. Lippold moved to Berlin from Prague around 1550 as mint master for Joachim, collector of his taxes, and manager of the privy purse. He also charged extortionate sums for private loans--sometimes as much as 50 percent.
As the confidant of Joachim, he was appointed governor of the Jewish community. He tyrannized over the Jews, extorted money from them and did not scruple to rob the widow and children of his brother. Although he managed to accumulate a great fortune, whether by legitimate or illegitimate means, he was not the richest of the bankers or purveyors to the court; he was only the most hated.
It was Lippold's intimate personal relationship with Joachim that caused his downfall. On the night of the prince's sudden death (January 3, 1571) witnesses testified that they had seen Lippold hand him a goblet of wine. Johann, the prince's son and successor, who had reason to loathe Lippold for what he perceived as his pernicious influence over his father, needed no better evidence. On that very night he ordered th gates to Berlin barred to prevent Lippold's escape. Lippold was arrested and charged with murder; a rich arsenal of torture instruments produced a confession. Although he subsequently retracted his words, it was too late; on January 28, 1573, he was drawn and quartered in the presence of an avid multitude, and the Jews of Berlin were once again banished from the city. The fate of the court Jew was, then, no private matter; a fallen court Jew could carry a whole community down to destruction with him. However execrated he may have been, Lippold dead brought a worse fate on the heads of his fellow Jews than Lipppold alive.
As mentioned before the position of "court Jew" brought with it responsibilities, powers, dangers and prominence which affected the individual and community alike for serious good or bad. The intercession of a respected individual could defend from allegations and intended evil, whereas a fallen or disrespected individual could bring great harm.
The fact that Jewish individuals were so limited in what occupations they could engage in, caused many to be involved in money-lending. We can imagine all the negative feelings which could be aroused by this occupation where Christians were not allowed to participate in "usury". Josel had obtained permission from Charles V that Jews would be allowed to charge much higher interest rates than Christians because they could not engage in other work and were required to pay higher taxes. Here we see the bind: Jews need to make a living. They made it often through money-lending, since they were limited in their options. They had to charge this interest to people who worked hard physically and also tried to make a living, perhaps at times squeezing it from stones, so to speak, so they could hand their own taxes to the Emperor. We can see that the Emperor who protected the Jews also was rewarded through this arrangement. This worked, in a way, for all involved, except for those who paid the high interest rates. One can understand their feeling of oppression.
This image appears later on on Ruth Gay's book. I am sure I have no copyright, so I will print it the smallest I can. It says: "O God, thou giver of the good and true, Save me from this very Jew." We see the farmer with his scythe, obviously a hard working family man, in front of the farm which has crosses on top of the roof, (so now we know it is a hardworking Christian man) with the Jew approaching, well dressed in black, in aggressive posture. It looks like he is going to force money out of the hard working, Christian, family man, farmer.
This is just to illustrate the chain of pressures placed on people. And this is just one of the complexities.
To illustrate this a little further, again from Ruth Gay, pp. 165 and 166:
How the Jews made their living by the time of the empire [Prussian] had been determined long before by a history of permissions and prohibitions. Their exclusion from landownership had made them traders rather than cultivators in rural districts, and their exclusion from the guilds had made them middlemen rather than craftsmen. Above all, Jews had been identified with the lending and exchange of money, as Hans Sachs showed in his True Description of All the Classes on Earth, published in 1568. It was a place in the world that had endured for a very long time. Even Moses Mendelssohn wrestled with these constraints as he confided to a friend about his son Joseph. "He has no inclination for medicine," he wrote in 1785, "and as a Jew he must become a physician, a merchant, or a beggar." Begging was, indeed, a fixture in Jewish life. For centuries the Jewish condition had insured that there were a very small number of rich Jews and an overwhelming number of poor ones. The beggars, in fact, formed a caste unto themselves with carefully apportioned territories, rights, and expectations. The schnorrer, as he was called in Yiddish, who was the subject of endless jokes and legends, was at once a beggar and more than that. In his circuit of villages and houses, he brought news of the world, gossip, and commercial information... As late as the mid-nineteenth century, half the Jews of Germany were either beggars or a step away from it, without a permanent right of residence.
These prohibitions had been in place for a long time. The money-lending could never be popular. The medicine could be suspicious, and all this before modern medicine and a scientific approach. A beggar and a wandering "schnorrer" would really be a kind of vagabond. Thus we understand that the Jew was forced into an unenviable position of severe limitation, inviting ostracism, abuse and anger.
The Jew was also under the protection of the Emperor rather than the local nobles. This would cause other frictions and understandably in Lutheran lands, who were under threat of Charles V themselves. During the Schmalkadic war, the Jews provided sustenance to Charles V's troops.
Back to Josel of Rosheim: this is what Martin Brecht has regarding his interactions with Luther.
In 1533 Luther showed an understanding of why the Jews had not been won by the papacy, and he hoped to convince many of them by preaching the gospel. In contrast, however, he thought debating with them held no promise. Since 1432 Jews had been forbidden to take up permanent residence in Electoral Saxony. It is unclear why Elector John Frederick issued a mandate at the beginning of August 1536 that prohibited them from staying there, engaging in business, or passing through...
In 1537 Josel of Rosheim, who at the time served as sort of a spokesman for Jews in Germany, tried to persuade Elector John Frederick to rescind the mandate of the previous year. A recommendation from Luther would gain him an audience with the elector. Wolfgang Capito interceded with Luther on Josel's behalf. this may ot have beenthe first time that Josel had written to Luther. Luther declined to support Josel's cause with the elector because his advocacy of the Jews in That Jesus Christ Was Born a Jew had been misused and the Jews had called Christians "apostates". Luther was still in favor of benevolent treatment of the Jews, in order to win them for the Messiah, but he would no nothing to confirm them in their error. He mentioned that he was intending to write a new pamphlet for this purpose. He had been asked to do so years earlier.
Luther attempted to explain to Josel that the Gentiles, who were enemies of the Jews, would not worship the Jewish king, not to mention a crucified Jew, if God had not done this. The Jews' suffering would come to an end only if they joined with the Gentiles in accepting this Christ, their "cousin and Lord." Luther mentioned the rejection of Christ in the rabbinic writings. For him, this was a continuation of the persecution of the saints and prophets in the Old Testament by their own people. It was unmistakable for Luther that the messianic prophecies could refer only to Christ. Finally, Luther maintained: "For the sake of the crucified Jew, whom no one will take from me, I gladly wanted to do my best for you Jews, except that you abused my favor and hardened your hearts."
Luther's letter to Josel has been seen as a turning point in his attitude toward the Jews, but this is hardly accurate. A little later Luther praised the advantages of the chosen people, although he did not fail to mention that they were of no avail before God. In the letter to Josel itself he stated his positive interest in winning the Jews to the Messiah. Alongside this was a polemic against the rabbis who rejected the Messiah. He also mentioned negative experiences of Jewish agitation against Christians. This situation must have existed for several years. Thus the letter to Josel did not indicate a break. Incidentally, the elector's mandate of 1536 was modified in 1539 through Josel's intervention, so that Jews were again permitted to travel through Electoral Saxony. (Brecht. Luther: The Preservation of the Church. p. 336, 337.)
So much for today. More can be found about Josel of Rosheim on wikipedia and other places.
On this site, a little further down are pictures of the synagogue and the church in Rosheim, Alsace. The church of the middle ages features a figure of a Jew with the moneybag. This is both indicative and sad.
Josel of Rosheim's autobiography might be very good reading, if it is available.