Mechagodzilla is a fictional mecha character that first appeared in the 1974 film Godzilla vs. Mechagodzilla. In its debut appearance, Mechagodzilla is depicted as an extraterrestrial villain that confronts Godzilla. In subsequent iterations, Mechagodzilla is usually depicted as a man-made weapon designed to defend Japan against Godzilla and other kaiju. In all incarnations, the character is portrayed as a robotic doppelgänger with a vast array of weaponry, and along with King Ghidorah, is commonly considered to be an archenemy of Godzilla.

In science fiction, mecha or mechs are giant robots or machines typically depicted as piloted and as humanoid walking vehicles. The term was first used in Japanese after shortening the English loanword 'mechanism' or 'mechanical' , but the meaning in Japanese is more inclusive, and 'robot' or 'giant robot' is the narrower term.