Following its founding in 1920, the NFL first determined champions through end-of-season standings, but switched to a playoff system in 1933. The rival All-America Football Conference (AAFC) and American Football League (AFL) have since merged with the NFL (the only two AAFC teams that currently exist joined the NFL in 1950—the Cleveland Browns and the San Francisco 49ers), but AAFC championship games and records are not included in NFL record books. The AFL began play in 1960 and, like its rival league, used a playoff system to determine its champion.
From 1966–1969 prior to the merger in 1970, the NFL and the AFL agreed to hold an ultimate championship game, first called the AFL-NFL World Championship Game and later renamed the Super Bowl after 1968. Following the merger in 1970, the Super Bowl name continued as the game to determine the NFL champion. The most important factor of the merger was that all ten AFL teams joined the NFL in 1970 and every AFL championship game and record is included in NFL record books. The old NFL Championship Game became the NFC Championship Game, while the old AFL Championship Game became the AFC Championship Game. The NFL lists the old AFL/NFL championship games with "new" AFC/NFC championship games in its record books. The Green Bay Packers have won the most championships with 13 total (9 NFL championships pre-merger, four (4) Super Bowl championships). The Packers are also the only team to win three consecutive championships, having done so twice (1929–1931, 1965–1967). The Chicago Bears have won the second most overall championships with nine (9) (eight NFL championships, one Super Bowl championship).
At its inception in 1920, the NFL had no playoff system or championship game: the champion was the team with the best record during the season as determined by winning percentage, with ties omitted. This sometimes led to very unusual results, as teams played anywhere from six to twenty league games in a season, and not all teams played the same number of games or against league talent.
As a result, in the league's first six seasons, four league titles were disputed and had to be resolved by the league's executive committee. In 1920, the Akron Pros went undefeated, tying three games, but two teams that had won more games (and who had both tied Akron), the Buffalo All-Americans and Decatur Staleys, petitioned the league for a share of the title; both teams' petitions were denied, and Akron was awarded the first (and only) Brunswick-Balke Collender Cup. According to modern tie-breaking rules, Akron and Buffalo would be co-champions. Akron and Buffalo both awarded their team members with gold medallions.
The next was in the 1921 NFL season, between the same All-Americans and Staleys (with the latter now being based in Chicago). Buffalo had insisted that the last matchup between the two was an exhibition game not to be counted toward the standings, however, Chicago owner George Halas and league management insisted the game be counted in its standings (the league, at the time, did not recognize exhibition matches). The result was that although the two teams were effectively tied in the standings, the disputed game, having been played later, was given more weight and thus ended up being considered a de facto championship game. Chicago also had one fewer tie game.
A nearly identical situation recurred in 1924, when Chicago tried the same tactic of a final game against the Cleveland Bulldogs, but the league ruled the opposite and declared the last game "post-season", giving the Bulldogs their third consecutive league title.
The fourth and final disputed title was the 1925 NFL Championship controversy between the Pottsville Maroons and the Chicago Cardinals. The Maroons had been controversially suspended by the league at the end of the 1925 NFL season for an unauthorized game against a non-NFL team, allowing the Cardinals to throw together two fairly easy matches (one against a team consisting partly of high school players, also against league rules) to pass Pottsville in the standings. The league awarded the Cardinals the title, one of only two in the team's history, but the Cardinals declined the offer and the championship was vacated.