The Atom is one of the playable in-game characters in LEGO Dimensions 2: The Rise of Enoch, from the DC Comics franchise.
Born in Hong Kong, Ryan Choi was a longtime protégé of Ray Palmer who had been corresponding with him through letters. After Palmer's disappearance, Ryan moved to Ivy Town in America to assume his mentor's place on the staff of Ivy University. Following clues left by Palmer, Ryan discovered a "bio-belt", allegedly the size and density-manipulating device used by his predecessor, and became the new Atom with Palmer's apparent blessing. Though taken with the superhero lifestyle, Ryan is a scientist first and foremost and approaches many of his adventures from the perspective of scientific discovery and investigation.
Since taking his mentor's place, Ryan has found himself at the center of a conflict between the forces of science and magic. It has been claimed that the impossible feats performed by Ray Palmer during his superheroic career caused the very fabric of reality to warp in Ivy Town's vicinity, making it a nexus of paranormal activity. Many parties, including the ancient "Cancer God" M'Nagalah and the microscopic aliens known as "The Waiting", consider Ryan a key player in the war and have made attempts to recruit, capture, or kill him. He is advised by among others Ivy Town Police Chief, Liza Warner (a.k.a. Lady Cop).
As The Atom, Ryan has faced numerous challenges, including the shrinking serial killer Dwarfstar, his strict and disapproving father, and being seduced, kidnapped, and even swallowed alive by the size-changing villainess, Giganta. Through it all, his ingenuity and keen deductive mind have served him in good stead.
Ryan Choi was involved in the search for the missing Ray Palmer, traveling into the restored Multiverse along with Donna Troy, Red Hood and a Monitor nicknamed "Bob". Literally plucked back to New Earth, he leaves his role of dimension-hopper to Kyle Rayner, returning to defend Ivy Town from a monster invasion. Later he is led to a mistaken belief that Ray Palmer has become an egocentric madman, and Ryan himself may be only a pawn of his mad fantasies. This is later revealed to be a ploy by Ray's old nemesis, Chronos. Ryan, with some help from the returned Ray Palmer, was later able to discern between the truth and the lies fed by Chronos and his new assistant, Lady Chronos, a former sweetheart of Ryan who turned to a life of crime. Ryan eventually discovers that Ray Palmer never knew of Choi: instead the bio-belt was a tainted gift from Jia, and the Ray Palmer letters a clever forging by Chronos, meant to force Ryan into accepting the Atom mantle, and taking the blame for the staging menaces sent against the city. However, due to Ryan's ability into sorting out the mess, besting the Chronos couple and restoring Ivy to normalcy, Ray finally gives him his blessing.