Captain Atom debuted amidst the the Cold War when atomic power was a scary prospect. He was revived and had a three year run until 1967, when another Captain... this one from outer space... was introduced at Marvel Comics. This Captain was inspired by a different contemporary topic... space exploration! Both liked that stars and Starlin!
Mar-Vell was a military captain, much like Atom's civilian identity, only he was sent by his race the Kree to Earth. At first an agent for their interests, he ultimately turned his attention to the affairs of the humans. In the process of doing this he changed his costume and gained cosmic energy manipulation powers which included superhuman strength and intense radiation discharges.
He also gained a human alter ego, of a kind, in Rick Jones whom he traded places with from his universe and that of the Negative Zone. His run didn't last much longer than had Captain Atom's, and ultimately he was doomed to an early death thanks to toxicity obtained from a villain. Meanwhile one of Cap's inspirations over at Charlton Comics was immune both to toxic substances and to cancellation of his titles.
Next week we turn our attention back over to the MLJ crowd with a two-for-one, as we're keeping that entry "all in the family":