Captain John Yossarian is the protagonist of the 1961 novel Catch-22 by Joseph Heller. He is a part of the 256th squadron of the Army Air Corps (which later became the US Air Force), where he acts as a bombardier. The character is based off of the author; for example, Heller was a bombadier in the Air Corps stationed on an island off the coast of Italy during World War II, and also lost crew members when his plane was attacked on his flight to bomb the city of Avignon.

His first name is never given in the book version of Catch-22; it was first used in the movie.

Yossarian is also the protagonist of Catch-22's sequel, Closing Time, which was published in 1994.

Although the book describes him as being Assyrian, his name indicates an Armenian background.

Throughout the book, Yossarian's main concern is the idea that people are trying to kill him, either directly (by attacking his plane) or indirectly (by forcing him to fly missions). Because of this, Yossarian avoids flying missions as much as possible, either through feigning illness or inventing an excuse to return to base (like a busted radio). In fact, the book begins with Yossarian staying in the hospital due to a liver condition.

Yossarian is also haunted by memories of the final moments of Snowden, one of his crew. Snowden, through his death, showed Yossarian that man is mortal. Because of Snowden's death, Yossarian becomes reluctant to fly missions, as it could ultimately result in his death, as it was with Snowden's.