Joe Gill and Steve Ditko had been enlisted by Archie Comics under their Adenture Series (successor to MLJ and precursor to Mighty) in 1959 to create Lancelot Strong, who as an infant had been experimented on by his father Malcolm to access the untapped potential in all humans. As a result, he was able to absorb energy and then emit it into a bio-electrical force, as well as great strength and flight.
Yes, both faced strange aliens early in their career, not surprising considering the American public's fascination for space travel during this period of time. Using innate, almost instinctual, mastery over fundamental forces, allowing them to soundly defeat such threat within the span 8 or 9 pages. Another typical Silver Age trend.
Lancelot had himself faced tragedy an an infant orphan, and was adopted by a loving farm couple who raised him as their own (hmmm). As a young man, he was enlisted into the military under the rank of private. Captain Adam, having a non-descript adolescence apparently, fast tracked his military career, and when first we meet him he is already a captain. Adam adopted a new career as the military's not-so-secret weapon, whereas Lancelot kept his double identity a secret for a time. When they were each revived years, both were Captains.
For Captain Atom, the reason he was placed on the shelf until the mid-60's was the departure of Ditko. For the Shield, it was legal troubles due to some similarities with a certain Man of Steel (no not him or him ).
During his mid-60's revival over at Charlton, Captain Atom was one of their headliners, while the Shield was replaced by a modern-day version of the original Shield. As such, it took a couple more decades for Lancelot to regain his own featured title and then he lost it...once more thanks to a Man of Steel (yes .that one).