Blood

In single-player mode, the player takes the role of Caleb in his quest for revenge against his former master by navigating levels in episodes, looking for an exit, until the boss level.

Blood's gameplay is similar to other classic FPS games like Doom: the player must activate switches or seek keys to go through the levels; some larger maps contain up to six different keys. Features include teleporters, traps such as crushing blocks, explosive barrels, lava pits, jumping puzzles, and combination lock doors.

Blood takes place in an unspecified time period. The various levels contain elements from the 1920s, 1930s, and 1940s, in addition to futuristic and retro-futuristic technologies and a weird West theme. Many elements are anachronistic, including weapons and pop-culture references. The sequel, Blood II: The Chosen, retroactively dates the game to the year 1928.

The backstory is not delineated in the game itself, only on the Monolith website and a readme text document. The player takes on the role of Caleb, once the supreme commander of a cult called "The Cabal", followers of the forgotten demon Tchernobog. Known as a merciless gunfighter in the late 19th century American West, Caleb joined the Cabal in 1871 after meeting Ophelia Price, a woman whose husband and son may have been murdered by the members of the Cabal; it is implied that she later became Caleb's lover. Together they rose to the highest circle of the dark cult, "The Chosen", until all four members of The Chosen were betrayed and killed by Tchernobog for unspecified failures. Several years later, Caleb rises from his grave, seeking answers and vengeance.

Development began at Q Studios, an independent developer funded by 3D Realms, in parallel with a number of other well-known titles. It started development in 1995. Following the success of Duke Nukem 3D, development progress was made public starting in June 1996 with weekly updates on their website. It was originally scheduled for release in early 1997.

Q Studios was acquired by Monolith in November 1996. On January 22, 1997, all rights had been sold to Monolith so that 3D Realms could focus efforts on Shadow Warrior, another Build engine game slated for release the same year. Ports for the PlayStation and Sega Saturn were planned but never completed.

Blood received "generally favorable" reviews from professional critics, according to review aggregator website Metacritic based on seven reviews. Critics especially praised the intricate and creative level designs, humorous wisecracks and pop culture references, over-the-top gore, variety of settings, and inventive, unconventional weaponry. GameSpot particularly noted that the voodoo doll "might be the coolest little accessory to ever grace the weapons belt of a first-person killing machine".

A few criticisms were voiced about the game, but did not find consensus among reviewers. For example, while GameSpot said the game "is just too damn hard", citing how quickly enemies can deal damage, Next Generation asserted that "the game is lengthy without being too tedious, and challenging without being too difficult". GamePro followed up its own criticisms by concluding: "Blood's flaws are easily swept aside when your guns start blasting and the bodies start falling".

Blood has received numerous fan homages and remakes, including Transfusion, ZBlood, BloodCM, and The Flesh Game, as well as community produced source ports such as BloodGDX, NBlood and Raze, and mods for other games such as the Bloom mod made for GZDoom. The game has also inspired several later boomer shooters such as Eternal Damnation, Viscerafest, Dread Templar, Coven, Nightmare Reaper, Project Warlock, Dusk, and most notably Cultic. It was also influential on the roguelike game Infra Arcana.

The manhwa series Priest created by Hyung Min-woo was inspired by Blood. An interview with Hyung in Priest, Vol. 3: Requiem for the Damned states that the comic was influenced by the game, which featured a similar horror-Western aesthetic and undead protagonist. The manhwa was adapted into the 2011 American horror film of the same name.