-Tjorbjorn is Engineer's grandfather who couldn't quite figure out how to get his turrets to Stage 3 without the use of his Molten Core.
-Heavy was Zarya's uncle (born from Soldier and Heavy's sister) who taught her to hate robots after the Gray Mann's mechanical invasion.
-Pyro wanted an equal match to his evil, so he molded Mei to counter his fire with her ice.
-Widowmaker is Spy's daughter, born from Scout's mother. Spy raised her to be a long range assassin with the help of Sniper, failing to foresee they created a monster.
-Medic was Mercy's father who taught her 1001 ways to harvest a spleen, but Angela saw it as fairy tales and decided to make her own way of healing.

Just a couple of headcanons I have for Overwatch and TF2 :)