Gideon Prewett was a member of the original Order of the Phoenix. Along with Fabian Prewett, one of the brothers of Molly (Prewett) Weasley (JKR, OP9), they were, according to Hagrid, among the “best witches and wizards of the age” who were killed during the first wizarding war (PS4). It took five Death Eaters, including Antonin Dolohov, to kill Fabian and Gideon (OP25). Moody said they died like heroes (OP9).
In the Hebrew Bible, Gideon was a leader who fought for his people's freedom from their enemies and the ideology of those enemies (Book of Judges).
Gideon and his brother Fabian both seem to be named for ancient military leaders who led underdog armies to victory (sources: Book of Judges, Wikipedia). -BB