From Legion Wiki
However, Halk Kar was left Krypton's orbit just as the planet exploded. The force of the blast knocked Halk Kar unconscious, leaving his ship to drift through space until in managed to reach Earth on its own.
Arriving on Earth, Halk Kar's spaceship was intercepted by Superman who, interpreting the note signed by Jor-El, declared the traveller, now afflicted with amnesia, to be his long-lost older brother.
During an adventure pitting the super brothers against the gangster Wrecker Ross, Halk Kar was electrocuted, which only served to restore his memory.
Once he realized that he was, in fact, no relation to Superman, Halk Kar blasted off into space to resume his quest of exploration.
Powers and abilities
Halk Kar possessed all the powers of the Earth-2 Superman, only to a slightly lesser degree. Halk later theorized this was because his home planet, Thoron was slightly smaller than Krypton. (At this point in the mythos, the yellow sun rational for explaining Superman's powers had not been concocted, leaving the difference in gravity between Earth and Krypton as the main explanation for Superman's fantastic abilities.)
Halk Kar's costume was the chromatic opposite of Superman's, with a red suit and a blue cape, boots, and trunks.
Halk Kar is included in the Legion Wiki because his origin story was later rewritten, forming the main plotline when Superboy's "older brother," Mon-El, debuted in Superboy v1 #89 (June, 1961).
Although this story itself was never contradicted specifically, there were several changes in the rewrite. Mon-El had the same powers as Superboy, rather than Halk's reduced powers. Halk had no known weaknesses, while Mon-El was famously allergic to lead. And, of course, Halk did not end up trapped in the Phantom Zone, which had not yet been conceived.
Into the Multiverse
This story was printed during the Atom Age of comics, a period after the Golden Age but before the universally accepted start of the Silver Age in 1956. However, many fans consider this tale to be an Earth-2 story.
Given his similar appearance, and how this story was later adapted, Halk Kar is often thought of as the Earth-2 Mon-El, even though there was never an Earth-2 Legion of Super-Heroes.
- Superman v1 #80 (cover, 45 panels - 2 in flashback)