Unless you are an above average Pittsburgh Steelers fan, you have never heard of Ted Doyle. He played at a time when almost no players had an agent to negotiate their contracts or represent them. If a player was represented at all, it’d often be a family member.
However, agents did exist even early in the NFL’s existence. Red Grange engaged C.C. “Cash and Carry” Pyle to negotiate his contract in 1925 with a professional football team while in college. The Galloping Ghost signed a contract with legendary George Halas of the Chicago Bears one day after his final college game with Illinois.