Knockout Kings is a series of boxing video games that were produced by EA Sports for the PlayStation, Nintendo 64, PlayStation 2, Xbox, Game Boy Color and GameCube yearly between 1998 and 2003.

Before releasing the first Knockout Kings, Electronic Arts released its first 3D boxing game, Foes of Ali, for the 3DO in 1995. While there are a few similarities between the two games, Foes of Ali was developed by a different team, Gray Matter and as such, is not regarded as a true prequel.

The Knockout Kings game series gives the user a chance to compete against numerous real fighters, such as Muhammad Ali, Eric Esch, Marvin Hagler, Sugar Ray Leonard, Oscar De La Hoya, Larry Holmes, Jake LaMotta, Roberto Durán, Alexis Argüello, and Ray Mancini. The duration of a round can be adjusted to either 90 seconds or 3 minutes. In the game's "slugfest" mode, fighters can knock each other out at any given moment of the fight, or suffer 6 or 7 knockdowns and still last for the whole fight. There are several differences between Knockout Kings, Knockout Kings 2000, and Knockout Kings 2001 in particular, the most notable being the graphics.

In Knockout Kings, the boxer sprites, although distinctive, are not facially representative of their real-life counterparts. Championship bouts can last only up to 10 rounds and not for 12 as in real life or 15 as in the past. In between rounds, all that is seen is a ring-card girl. In Career Mode, a fighter is made to retire right after winning the title and defending it for only the first time. A created boxer can fight in Career Mode and Slugfest Mode, but not in Exhibition mode. Although there is a training mode within Career Mode, it is extremely basic. However, 2 aspects that Knockout Kings has which the sequels lack is that the referee does a mandatory eight-count when a fighter is knocked down whereas in the sequels the referee stops the count immediately after a fighter gets up from a knockdown, and, in Career Mode, the result of a fight is afterwards seen on the screen as front-page newspaper headlines.

In Knockout Kings 2000 for the PS1, the boxer sprites are for the first time facially representative of their real-life counterparts. Championship bouts can last up to 15 rounds. Sound and Music volume can also be adjusted in Option Mode. In between rounds, you may see either a ring-card girl, a replay of a part of the previous round, or your boxer sitting at his corner together with the statistics so far of the bout. Injury to the face of boxers can also be recognized, as well as his mouth-piece flying out if he is hit by a hard punch. A created boxer in Career Mode can now fight in all Modes. The training mode within Career Mode is more specific. You can now control your boxer while he is training and, in the PS1 version, you can also choose the location of your gym. Each boxer in the PS1 version can also be seen entering into the ring just before the bout takes place. There is also a new Mode where the player can see the statistics and biography of all the real-life boxers in the game, and another Mode in which the player can re-live famous classic bouts. The user-interface and intro-theme of the PS1 version is different to the N64 version and there are also more boxers, while the graphics on each version are similar.

Knockout Kings 2001 contains the same improvements as Knockout Kings 2000 and adds more. Whereas fighters in KO Kings and KO Kings 2000 are either "boxer" or "slugger" style fighters, the styles of fighters in KO Kings 2001 are either "boxer", "slugger", "freestyle", or "crab", and these differences of style are very noticeable during bouts. Commentary in KO Kings 2001 is also far more vocal than its predecessors. During Career Mode, your trainer will occasionally talk and give you advice in between rounds as you progress through the bout. A fighter in Career Mode is made to retire after winning the title and defending it for several times. KO Kings 2001 is also the first game of the series to introduce CPU vs CPU bouts and "fantasy match-ups" between famous boxers of different eras, and the first to introduce women's boxing, which is accessible in Exhibition Mode. The PS1 and PS2 versions of Knockout Kings 2001 are virtually identical.

Knockout Kings 2002 changes many concepts of its predecessors, e.g. you have to progress through a number of bouts in order to unlock new fighters.

After Knockout Kings 2003, the name of the series was replaced by Fight Night (EA video game series).