Sydney Palmer is the older brother of Ray Palmer. After his brother joined the Legends in their time travel, leaving 2016 and presumed dead, Sydney, in a potential future, acquired Ray's technology and continued his brother's work in robotic engineering, becoming known as the father of the robotics industry by 2147.
It has been implied that Sydney and Ray are identical twins, as their facial appearances are the same.
Sydney was born to David and Sandy Palmer in Ivy Town and had a twin brother, Ray. During his childhood, Sydney liked to play the video game Tecmo Bowl and often fought with Ray as the latter preferred to play Legend of Zelda.
In a possible future, Ray theorized that Sydney went to work for Felicity Smoak at Palmer Technologies, where at some point, he acquired his brother's A.T.O.M. Exosuit technology, claiming it as his own after Ray's disappearance. Sydney later sold his brother's research to the military.
Sydney passed on the Palmer name and his descendant, Dr. Bryce, continued his passion for robotics in the Kasnia Conglomerate, with a bust of him appearing in the lobby of the building she worked in. According to Bryce, Sydney was the founder of the company that would eventually produce robotic enforcers, dubbed A.T.O.M. robots by Ray, for the Kasnia Conglomerate.