The details of his life are unusually unclear for a painter of his significance at this date, despite the fact that his commissions show that he had reasonable recognition in his own lifetime. The first source for his biography is the German art historian Joachim von Sandrart, who describes him around 1505 working on the exterior decoration of an altarpiece by Albrecht Dürer in Frankfurt. This is the sort of work typically performed by apprentices and therefore an estimate of his age can be reached, suggesting he was born in 1475. Sandrart records that Grünewald had as an apprentice the painter Hans Grimmer, who became famous in his time, but most of whose works were lost in the Thirty Years' War. Sandrart describes Grünewald as leading a withdrawn and melancholy life, and marrying unhappily.