Mimic (Calvin Montgomery Rankin) is a fictional character appearing in American comic books published by Marvel Comics. He was briefly a member of the X-Men in the 1960s, and was the first character to be added to the team after the original line-up and the first X-Man who was not a mutant, though a 2019 story revised the character and identified him as a mutant.

An alternate reality version of Mimic became a popular member of the Exiles, the reality-hopping team.

Created by writer Stan Lee and artist Werner Roth, he first appeared in The X-Men #19 (April 1966) as a villain.

Calvin Rankin was born in Passaic, New Jersey. After an accidental mixup of chemicals from his father Ronald Rankin's experiments, his latent mutation activated and he gained the ability to temporarily copy the skills, physical traits, knowledge, and superpowers of any person within close range (approximately ten feet), which led people to fear him. When Ronald found out about this, he retreated with Calvin into a mine where his father worked on a machine which, as he claimed, would make the abilities his son absorbed permanent. However, these experiments with the device caused several power outages in the vicinity; to hold off the mob which was tracking these disturbances, Ronald blasted the mine entrance, but was accidentally caught and killed in the explosion, and the device sealed deep inside the mine.

Calvin first encountered the X-Men when he got into a fight with X-Men members Beast and Iceman in their civilian identities and duplicated their powers to defeat them. He later came across Marvel Girl, and found out her secret after gaining Marvel Girl's telekinetic power. Rankin decided to seek out the X-Men in a plot to get to the machine and make their powers his permanently. Taking the costumed identity "Mimic", he went to their mansion and battled the X-Men. He then escaped them, taking Marvel Girl hostage and drove to the mine, knowing the rest would follow. As the others came near, he regained their abilities, and he used Cyclops's optic power to break through the rubble to the machine. The other X-Men freed Marvel Girl and battled Mimic. Initially, he gained the upper hand and activated the machine after using Professor X's power to understand how the machine worked, but his powers were removed by Ronald's device, as Professor Xavier had expected. Xavier then wiped his memory and let him go.

It was while attending the same college as Jean Grey that his memory returned. In another attempt to gain the X-Men's abilities, Mimic set his sights on joining their ranks, becoming deputy leader in the process when he blackmailed his way into joining the X-Men. As a member of the team, he aided them against Banshee and Ogre of Factor Three, but soon began to antagonize the other X-Men with his arrogant behavior and ended up expelled after a fight with Cyclops. However, shortly afterwards he saved his ex-teammates from the Super-Adaptoid, defeating the android by tricking it into trying to copy his artificial powers. This battle robbed him of his abilities, and he was left powerless but a better person.

Eventually, Mimic regained his powers, but they were enhanced to also absorb people's life forces, killing them. As the Beast tried to work out a solution, Calvin seemingly perished in a self-sacrificial fight against the Hulk after absorbing Hulk's gamma radiation. For a long time, the X-Men believed him to be dead. In actuality, Mimic was in a coma which lasted for years. Mimic woke up when Wolverine came near him, because his power copied Wolverine's healing ability. Mimic also ended up copying Wolverine's other powers, including his claws, but after a confrontation with Wolverine, the Hulk (in his "Joe Fixit" persona) and an artificial intelligence remnant of his father, he began learning self-control by a meditation technique Wolverine taught him.

Mimic's powers soon began to drain the life energy of those around him again. He fled to a remote Siberian village, where he soon encountered X-Force investigating a distress call. X-Force arrived to find a number of dead scientists and the enraged Mimic who illogically blamed X-Force for their deaths. During the fight, Mimic copied Sunspot's powers, and their identical charge caused a large explosion, after which Mimic disappeared.