The character debuted on June 6, 2000, when the Angels were trailing the San Francisco Giants 5–4 in the bottom of the ninth inning. Two video board operators, Dean Fraulino and Jaysen Humes, took a clip of a monkey jumping around from the 1994 Jim Carrey movie comedy Ace Ventura: Pet Detective, and superimposed the words "RALLY MONKEY!" on top of it. The Angels scored two runs and won the game.
The video clip proved to be so popular that the team hired Katie, a white-haired capuchin monkey, to star in original clips for later games. When seen, she bounces to the House of Pain song "Jump Around" and sometimes holds a sign proclaiming that it is "RALLY TIME!"
The rally monkey came to national and world-wide attention during the Angels' appearance in the 2002 World Series, again against the San Francisco Giants. In the 6th game, the Angels were playing at home, but were trailing the series 3-2 and facing elimination. They were down 5-0 as the game entered the bottom of the 7th inning. Amid fervid rally-monkey themed fan support, the Angels proceeded to score 6 unanswered runs over the next two innings, winning the game and turning the momentum of the series for good (they went on to clinch the championship in game 7).
In 2009, the Angels once again reached the post-season, sparking a renewal of the rally monkey's popularity.
Additional videos featuring the Rally Monkey show her edited into popular films and TV shows such as Gilligan's Island, Shrek, Ferris Bueller's Day Off, The Brady Bunch Movie, Signs, Jurassic Park, The Price Is Right, Willy Wonka & the Chocolate Factory, Scream, Dumb and Dumber, National Lampoon's Vacation, Night at the Museum, The Natural, Austin Powers: International Man of Mystery, Spaceballs, Avatar, The Lego Movie, Poltergeist, Borat, The Sandlot, Psycho, Jaws and The Ring. The Angels started selling plush monkeys that fans bring to games.
ESPN did a SportsCenter commercial in which it showed one of the executives having to make "budget cuts," leading to the release of the monkey. The monkey pleaded by raising the "It's Rally Time" sign. The commercial is available on NFL 2K5 video game.
In one installment of the popular comic strip Get Fuzzy, the strip's protagonist, Bucky Katt, attempts to travel to Anaheim to eat the Rally Monkey after seeing it on television, as part of a running gag focused on Bucky's irrational desire to eat a monkey.