As with most figures from the Middle Ages, we don't have much certain information. It is known, however, that he was a German priest who later acted as an inquisitor in Germany. It was he who Pope Gregory IX appointed as the first inquisitor in 1231. We also know the exact date of his assassination by knights on July 30, 1233. Unfortunately, his inquisitorial activities were also not very commendable, he was considered a very harsh and unjust judge. There is also no certainty about his affiliation with the Dominican Order, as well as with the Premonstratensians (Norbertines) or Franciscans, although both in the tradition of these orders and in modern historiography one can find information that he belonged to one of these orders; the most common reference is that he belonged to the Order of Preachers. Nevertheless, most scholars dealing with the history of the Inquisition both in Europe and in Germany itself insist that he might simply have been a diocesan priest, and certainly fought heretics even before the Dominicans.
Conrad was born between 1180 and 1190 to a noble family. Nothing is known about his childhood. However, it is reported that he was well educated and that he possessed a great deal of knowledge. His contemporaries called him magister, which may indicate that he graduated from some European university of the time, perhaps in Paris or Bologna. He was also known for his tremendous asceticism and great zeal in defense of the Church. His pastoral work was primarily related to suppressing heresy, searching out and converting heretics. Between 1217 and 1221, he took part in the Fifth Crusade against the Albigensians in southern France, organized by Pope Honorius III. Conrad's supporter was the next Pope Innocent III. When he returned to his native country, Germany, he first became the spiritual director of Elisabeth of Hungary (1207-1231), wife of Ludwig, Landgraf of Thuringia. Allegedly, he was the one to persuade her to live a very austere lifestyle, as a result of which she died on November 17, 1231. Later, he was a witness in her canonization trial. That same year, he was appointed papal inquisitor in Germany by Pope Gregory IX. The pope also instructed him to take two helpers - Conrad Tors (Dors), a lay Dominican, and John, a diocesan priest. These two helpers became known for their particular cruelty, sending a huge number of people, not always heretics, to the stake. Conrad of Marburg himself was not renowned for his gentleness and honesty as well; he was accused of credulity, lack of reason and injustice. According to most accounts of the time, he believed almost all the accusations to be true and the suspects to be guilty of heresy. It was his associates who sought out suspects and, by threatening to burn them at the stake, forced them to repent for their deviation from the faith; moreover, they forced them to denounce others so they could preserve their lives. Conrad of Marburg was also accused of bypassing all the procedures prescribed by church law. For example, the local bishop did not sit on the Inquisition Tribunal, despite their objections. To ignore them, he was to receive permission from the Pope himself. Increasingly, complaints about his activities reached the Pope, who became concerned about them. Conrad's failure to apply the laws, however, it is not so clear, and there is still some debate among researchers as to whether he would break them or merely push the boundaries a bit, especially since the new inquisition laws were coming in a bit later in Germany. Notwithstanding, it is undisputed that such an opinion has permanently entered historiography.
Both commoners and nobles or clergy became victims of his inquisition work. Count Henry II also fell to his accusers. The latter appealed to Sigfried II, Archbishop of Mainz, who convened a synod specifically on the matter. It met on July 25, 1233 and acquitted the count. Conrad, however, refused to accept the synod's decision and demanded a verdict, but eventually resigned and left Mainz to return to Marburg. On July 30, while on the road, he was attacked by several knights and murdered. His death prevented the Pope from clarifying the charges against Conrad. Furthermore, the Pope declared him a martyr for the Christian faith, and excommunicated his killers, and then had them still punished.
After his death, his two associates, Konrad Tors and John, continued to pursue heretics. However, they too were murdered shortly thereafter. Still in 1233, Conrad was killed in Strasbourg, and John was hanged in Friedberg.
According to the legend promulgated by the Dominicans after his death, he was supposed to be a member of their order, recruited by St. St. Dominic, who sent him on a mission to Germany to combat heresy.
The depiction, located in the cloister garth of Lima's Santo Domingo Monastery, features an inscription stating that he is the first martyr inquisitor, in addition, it is emphasized that he bears the title of Blessed. The dagger at his throat suggests that his throat was slit. In the historical scientific literature to date, I have not been able to find an accurate description of his death.