This is a "Wild Mass Guess" entry, where we pull out all the sanity stops on theorizing. The regular entry on this topic is elsewhere. Please see this programme note.
Jaeger and his father come from a genetic line of bioaugmented SuperSoldiers.
Hence his Healing Factor, occasional berserker fits, and why those creepy guys in fingerprint masks were hanging round his family when he was a kid.
Jaeger is an alternate-universe version of Wolverine.
Short but tough guy with a Healing Factor, Jerk with a Heart of Gold tendencies, solitary except when he doesn't want to be, occasional berserker fits, and a non-creepy tendency to befriend teen girls...