The Monkey forms the compatibility trio with the Rat and Dragon in Chinese zodiac tradition.
Chinese zodiac compatibility traditions group some signs into trines, or three-animal harmonies. Rat, Dragon, and Monkey make one of the four traditional trines, often called the first trine.
These groupings come from traditional astrology and folk belief. Rat is associated with resourcefulness, Dragon with power and ambition, and Monkey with cleverness and adaptability in many popular interpretations. The trio is therefore often described as energetic, inventive, and goal-oriented.
Compatibility charts are not uniform across every modern source, and they are cultural systems rather than scientifically validated tests of personality. The trio itself, however, is a standard feature of common Chinese zodiac reference tables.