Ignatius Prewett was a pure-blood wizard and a member of the Prewett family. He is primarily known for his marriage to Lucretia Black, which connected his family to the House of Black. His name appears on the Black Family Tapestry at Number Twelve, Grimmauld Place. Through his familial connections, he was the uncle of Molly Weasley (née Prewett), Gideon Prewett, and Fabian Prewett, and the uncle-by-marriage of Sirius Black and Regulus Black.
Born in 1915, Ignatius was a member of the prominent Prewett family (J.K. Rowling's Black Family Tree). At some point, he married Lucretia Black, the sister of Orion Black, thus marrying into the Noble and Most Ancient House of Black. The marriage, which is recorded on the Black Family Tapestry, produced no children. Ignatius was the paternal uncle of Molly Weasley and her brothers, Gideon Prewett and Fabian Prewett (Pottermore). He lived through the rise of both Gellert Grindelwald and the first ascent of Lord Voldemort. While his nephews Gideon and Fabian were members of the original Order of the Phoenix and were murdered during the First Wizarding War, Ignatius's own involvement or allegiance during the conflict is unknown. Ignatius Prewett died in 1985 at the age of approximately 70, four years after Lord Voldemort's initial defeat (J.K. Rowling's Black Family Tree). The cause of his death is not recorded.
There is no information in the novels regarding the physical appearance or personality of Ignatius Prewett.
As a member of an ancient pure-blood line, Ignatius was presumably a capable wizard. However, no specific magical abilities, skills, or wand details are known.
There is no record of any significant possessions belonging to Ignatius Prewett.