Short answers, pulled from the story.
Pudge Heffelfinger was the first recorded professional gridiron football player, receiving $500 to play a game for the Allegheny Athletic Association against the Pittsburgh Athletic Club in 1892. The second paid player was Ben "Sport" Donnelly, who received $250 to play for the same team the following week. Both players denied the payments for much of their lives.
NBC broadcast the first televised professional football game on the 22nd of October 1939, from Ebbets Field. The game was between the Brooklyn Dodgers and the Philadelphia Eagles, captured by two fixed monochrome iconoscope cameras with a single commentator, Skip Walz.
The American Football League, which played from 1960 to 1969, introduced official scoreboard clocks, player names on jerseys, the two-point PAT conversion, gate and TV revenue-sharing, and the first cooperative television plan in which broadcast proceeds were divided equally among all member clubs. It also pioneered the use of moving on-field cameras and miked players during broadcasts.
The Arena Football League held a broad patent on its rules, collectively known as arena football, that it interpreted to block other indoor leagues from operating until 1997, when the Professional Indoor Football League successfully defeated the AFL's legal action. The one fully protected aspect, the large rebound nets used to keep balls in play, remained under patent until 2007.
Canadian football evolved on a parallel but distinct path from American football. The CFL uses a 110-yard field, retains goal posts on the goal line, allows only three downs, and has more liberal rules for the drop kick. These features are relics of the older rules the Canadian game adopted and kept, even as American football changed.
The United States Football League won its antitrust lawsuit against the NFL, but the jury awarded damages of only $3. The result was a Pyrrhic victory that effectively ended the USFL rather than forcing a merger or significant settlement.