He was the son of Robert Forster of London, a stockfish merchant. Elected Sheriff of London in 1444, he became Lord Mayor of London in 1454, and served as the city's Member of Parliament in King Henry VI's 13th parliament.[1] According to historian John Strype, Foster married a widow named Agnes, who enlarged Ludgate prison (where Forster had at one time been imprisoned for debt[2]) and improved conditions for those incarcerated therein.[3]