Bursting onto the scene, Robotman almost immediately achieves national attention when he visits Washington and witnesses the Atom and Dr. Mid-Nite battles a Mr. Hyde-type monster.  He sees their victory and fades into the shadows but trails them at a distance. He catches up to them as they answer a summons from FDR to mobilize against the Japanese and he along with several other heroes head to California in anticipation of a Japanese attack.  They fend off planes targeting San Francisco while in Hawaii, other heroes managed to revive the Justice Society and defeat Per Degaton, the time-traveling criminal behind these events (All-Star Squadron #1-3, Justice League of America #193).  Robotman then joins the All-Star Squadron and remains a highly active member through 1942.

An early challenge to Robotman came when a lawsuit was raised questioning whether he was an independent being or an unlicensed machine that need regulation and possible decommission as a danger to society.   Public opinion was split with some supporting Robotman based on his heroic activities but many fearing him as a monster or a menace.   Robotman allowed himself to be taken in chains and after many witnessed had recounted harrowing encounters with him, Robotman himself took the stand.  He revealed the full truth of his origins, that Robert Crane had not been truly murdered and that his brain living on in the shell he and Grayson he created.  At the height of the trial, the roof began to collapse causing the prosecuting attorney to suffer a heart attack. Robotman raced him to the hospital, saving his life.  When he returned to the court, he was met with cheers and the judges dismissal of the case and certification that he was a real, if highly modified, human being (Star-Spangled Comics #15, All-Star Squadron #17). Joan Carter, Crane's fiancee, was initially drawn to Robotman man but vanished out of his life soon after.  Chuck Grayson remain connected but also less frequently involved as Robotman attempted to maintain a life out of the public eye as Paul Dennis.

Much of Robotman's casework was routine criminals but he had some encounters with more advanced villains.  Early encounters included the Human Magnet - a criminal who wore a harness that could attract or repel metal (Star-Spangled Comics #9) and the Turtle, a criminal who manages to get his hands on advanced robotics (Star-Spangled Comics #17).   Later colorful foes include the cat burglar Tiger-Man (Star-Spangled Comics #54), criminal circus performer Rubberman (Star-Spangled Comics #77), the science-based criminal The Baffler (Detective #143) and a criminal brain in a robot body in Robotcrook (Detective #153).

In 1944, a sense of isolation inspired Robotman to create a companion for himself.  Using similar mechanics and a primitive form of artificial intelligence, he designs a robotic dog body and named it Robbie.  Initially, all Robbie could say was "Here I am" but that was sufficient to help Robotman capture thieves targeting the subway (Star-Spangled Comics #29).  A month later, Robbie was displaying a wider range of both vocal and basic analytical skills and his programming was beginning to operate more independently (Star-Spangled Comics #31).   He remained Robotman's companion and sidekick for several cases but after 1948, no recorded activities of Robbie exist. Whether the record is incomplete or something befell Robbie is not known.

In 1951, the House Un-American Affair Committee limited the actions of costumed vigilantes (Adventure Comics #466).  Some such individuals maintained relationships with local law enforcement that condoned their activities at a more limited scale.  Throughout the 1950's, Robotman largely stayed close to home, addressing mundane crimes.  On one hand, he used the time to experiment more with his robot body, doing things like adding extra arms (Detective Comics #156), attaching a crime lab to his body (Detective Comics #164) or even modifying himself to fight fires (Detective Comics #165). On the other, staying local limited what he could do when damaged when was frequent.  He at times had to rely on amateurs to help (Detective Comics #145, #175) and in one case, the repair shopped employed an ex-convict with a score to settle against Robotman (Detective Comics #183).

In the late 1950's, Robotman is on the trail of Alvin Lashky in Carver City when he is tricked into a rendezvous in a mine shaft that collapsed.  His robot body activates a fail-safe mechanisms to keep his brain safe and oxygenated by putting him into a state of suspended animation.  Twenty years later, he revives and continues his prosecution of Lashky only to find him an old man.  He nevertheless reveals Lashky's criminal empire but realizes that his time as a hero may have passed.  Learning that Chuck Grayson had died and left a cryopreserved body for him, he arranges to have a brain transplant into human form (the original purpose of the robot form) and live out the rest of his days in peace (DC Comics Presents #31, verified as Earth-Two in America vs. the JSA LS).