Ratchet: Deadlocked (known as Ratchet: Gladiator in Europe and Australia) is a 2005 third-person shooter platform video game developed by Insomniac Games and published by Sony Computer Entertainment for the PlayStation 2. It is the fourth installment of the Ratchet & Clank series. The game's story begins as Ratchet, Clank, and Al are abducted and forced to compete in "DreadZone", a violent game show in which heroes are forced to kill each other. Ratchet is given a "DeadLock" collar, which will explode if he becomes uncooperative or boring. The three must find a way to deactivate the collars and free the other heroes being held prisoner.

The gameplay is similar to that of other games in the series, but focuses more on shooter aspects rather than platforming. The player, as Ratchet, fights in DreadZone tournaments across the "Shadow Sector" in the "Solana" Galaxy, with a large variety of weapons. This game was the first in the series to feature cooperative gameplay in a story mode, and also includes an online multiplayer mode. Some vehicles return from previous games, and new ones are introduced. For the first time, Clank (in his typical form) was not a playable character.

Deadlocked was met with generally favorable reviews and was a commercial success, selling 2.1 million copies by 2007. A remaster developed by Idol Minds was released for the PlayStation 3 in 2013, separate from Ratchet & Clank Collection.

The gameplay of Deadlocked is similar to that of previous Ratchet & Clank games, with a combination of shooting, action, and platforming, although it emphasizes more on the combat aspects of the series, with little platforming. Deadlocked was the first game in the Ratchet and Clank series to contain an adjustable difficulty level, and is the first to have a cooperative story mode with two players.

The player controls Ratchet from a third-person perspective, although first-person play is possible, while competing in missions and tournaments, defeating enemies, and occasionally controlling vehicles. "Combat bots", two robots which follow the player in most missions, give Ratchet extra firepower, and perform several tasks for him, such as planting explosives and hacking orbs. Combat bots can be upgraded and given new paint schemes, head designs, and weaponry. After completing missions, the player is awarded a certain amount of "Dreadpoints" and bolts, the game's form of currency. Bolts can also be obtained by defeating enemies, or by locating hidden "Jackpot" crates across planets. Certain amounts of "Dreadpoints" are required to unlock new planets, and affect Ratchet's leaderboard rank amongst other contestants of DreadZone.

There are ten weapons in Deadlocked, fewer than most other games in the series. However, weapons can now be extensively modified using a large range of "Alpha" and "Omega" mods, which improve weapon abilities. Alpha mods improve statistics such as rate-of-fire and ammunition capacity, while Omega mods add a secondary effect to the weapons, such as napalm, or the ability to freeze enemies upon impact. While Alpha mods can be equipped on any weapon, some Omega mods aren't compatible with certain weapons; for example, napalm is only usable on weapons with explosive ammunition. As the player progresses, more weapons and mods become available, such as the "Arbiter", a rocket-launcher, and the "Scorpion Flail", a powerful melee weapon. Weapons and mods are purchased from vendors using bolts, which also sell ammunition. As weapons gain experience, they will upgrade to more powerful versions, and to a maximum level of 10 (99 in challenge mode). The game's health system, Nanotech, can also be upgraded through garnering experience by defeating enemies, and reaches a maximum level of 100 (999 in challenge mode). Whenever the player takes damage, it can be partially restored by breaking nanotech crates. In total, the game contains a maximum of 165 skill points which also reward bolts, and many extras which can be unlocked by performing certain feats.

Clank, Ratchet's robotic best friend, is only a playable character if his skin is unlocked, and cannot be used as a jet-pack device by Ratchet, unlike older games. Instead, he acts as mission control, giving the player advice during gameplay. A skin for a second player in cooperative mode, however, named "Alpha Clank", is used by default, but can be changed.

In cooperative mode, the second player takes the place of the combat bots. The bot's gadgets can then be used by the players instead, when necessary. Players in cooperative mode must share weapons and ammunition supply, and as a result, both players cannot use the same weapon at the same time.