Painkiller is a first-person shooter video game developed by Polish game studio People Can Fly and published by DreamCatcher Interactive in April 2004 for Microsoft Windows and ported to Xbox in 2006. The game's single player campaign follows a dead man in Purgatory who is offered a deal to defeat the invading forces of Lucifer's army in exchange for being allowed to enter Heaven. The game was particularly well-received for its multiplayer experience and was featured for two seasons on the Cyberathlete Professional League's World Tour. A reboot with the same title has been announced for release in October 2025.

The game is inspired by first-person shooters such as Quake, Doom and Serious Sam, with the emphasis on killing large numbers of monsters. The game is divided into five chapters, each about five levels long. The player's objective is to get through each level, from start to finish, by slaughtering hundreds of monsters. Fighting monsters often occurs in mass battles, where the player has to fight an attack by a swarm of enemies in a large room, while the exits shut and heavy metal music plays in the background, and after such a battle, the player passes a "checkpoint" which advances the game, the exits open up again, and the music returns to the usual softer tune played in the level. One of the game's most important aspects is its diversity, with each level presenting a new location with various themes and graphic styles. The levels include castles, monasteries, an opera house, graveyards, and more. Monsters are also very different, with new ones almost every level. There are five "boss" levels where the player fights a boss.

The game presents an option to complete a special task each level, which results in the player getting a "tarot card", a rare, hard-to-obtain bonus. Each equipped card provides different bonuses for a small amount of time (30 seconds), like powered-up weapons or slow motion.

The game also features a multiplayer component which can be played via LAN or online. It includes classic modes like Deathmatch and Capture-the-Flag. Online support for the Xbox version shut down in April 2010, although it is now playable on the replacement Xbox Live servers called Insignia.

The game revolves around a young man named Daniel Garner (Cam Clarke), who is happily married to his wife Catherine (Vanessa Marshall). At the start of the game, Daniel is about to take Catherine out for a birthday meal. As they drive towards their destination at high speed, in the pouring rain, Daniel takes his eyes off the road to look at his wife and while his attention is diverted, he ploughs their car into a truck. Both of them are killed instantly in the crash.

While Catherine manages to make it to Heaven and lives in harmony, Daniel is trapped in Purgatory. One day, an angel called Samael (John Cygan) tells him that in order to receive purification, he has to kill four of Lucifer's generals in order to prevent a war between Heaven and Hell. Lucifer has been secretly organizing a massive army that could overwhelm Heaven, taking over Purgatory in the process. Small portions of the army are already beginning the march. With little choice available to him, Daniel accepts the task. With the forces of Hell seizing and corrupting various parts of Purgatory, Daniel goes through different and random phases of history within Purgatory, which range greatly from ancient times to the modern era, including Medieval Europe, Babylon, the Crusades, the 1800s, and a time slice of modern industry.

After killing the first general, Daniel meets a woman named Eve (also voiced by Marshall), another soul who has been in Purgatory for a long time. She gives him information about the whereabouts of the remaining generals and small elements of Lucifer's army already mobilizing. She also tells him about life in Purgatory, and the possibility that he could be dragged to Hell should he fall in battle and become lost forever. While this is all understood, what Daniel does not understand is why he came here, but Eve insists it is because of something in his past, and it is up to him to find out.

After the second general's defeat and reuniting with Eve, Daniel travels to meet a demonic friend named Asmodeus (Jim Ward), for information about new rallying positions for Lucifer's armies. Asmodeus once saved Daniel's life after he single-handedly defeated four demons at once one day, almost losing himself in the process. Eve is wary of Asmodeus and questions as to why he did not finish off Daniel when he was weak, but he insists that he did not come to Purgatory to fill the graves with lost souls like the others. He also questions Eve if she is really "The Eve" referenced in the Bible, to which Daniel jokes "Where is Adam?" before continuing on.