Marshall Cooper is considered to be one of the most influential figures in the history of The League. His legacy in The League included time as a player, commissioner, and competitor.

Cooper played for the Chicago Scouts as a running back during The League's inaugural season in 1916. The following year, he, along with the vast majority of young men playing in The League, was drafted into the military for World War I, halting Tobias Walker's fledgling league.

While serving in the military, Cooper was promoted to lieutenant, and quickly earned status as a war hero, as he was thrice decorated for valor. He also served as something of an ambassador for football, organizing impromptu games with his comrades on the battlefield during breaks in fighting. Even the enemy German military became captivated with the game, and joined in at times.

After the war, Cooper helped Tobias Walker start The League once more. In 1923, The League was re-launched with six teams, and Walker and Cooper serving as co-commissioners. This agreement went well until 1929, when Walker died from a stroke. Walker's interest passed to his brother, Judge Hugh Walker. Hugh did not approve of the violent, unstructured style of play that Tobias and Cooper allowed, and began implementing additional rules and penalties. Unable to sway Judge Walker otherwise, Marshall Cooper resigned his position as Commissioner.

In 1932, with The League suffering at the gate and on the field under Judge Walker's rules, Cooper started his own five-team league to compete with Judge Walker, keeping the original rules and spirit of his and Tobias' old League. The two leagues competed and co-existed until 1936 when, following a brawl between the two New York teams in each league, Cooper and Judge Walker agreed to let the teams play, with ownership of both leagues at stake. On New Year's Day of 1936, the New York Dutchmen of Cooper's league defeated the New York Shamrocks of Judge Walker's league, assisted by a shift in the rules to Cooper's rough and tumble style in the second half. Hugh Walker was forced to sell his league to Cooper and leave the game of football forever. Rather than merge the leagues outright, Cooper decided the teams in Walker's league would have to move up and fight for the right to play the teams in his league. Cooper therefore introduced the two-division system of play for the first time.

In 1942, war once again interrupted The League and put an end to Cooper's innovative division system. World War II saw a large amount of players drafted or volunteering for military service, so Cooper was forced to contract The League. Cooper shrank the number of teams in The League from twelve to six, and moved several teams into larger, more diverse markets.

Marshall Cooper died in his sleep in 1947. Upon his death, his son Guy became The League's new Commissioner.