Conrad Kellogg

Kellogg is a very powerful opponent, with decent armor and (depending on player character level) generally more than twice as much health as an NPC companion.
Technically, Kellogg is one of the oldest characters in the Fallout series when not accounting for non-human characters (such as ghouls, super mutants or Harold) or humans who spent their lives in extensive cryogenic supports (such as Robert House, Sole Survivor, Stanislaus Braun), although Kellogg's age is a result of cybernetic improvements