Pull a page out of Disney’s book: dead parents.

In what way could this character have lost his parents in this universe? Vary the emotional damage to fit the theme you want (you can even have the character’s parents die in a stupid way if you want the story to be somewhat humorous)

Create a villain (or hero) to have committed that act—or use factions you already thought of—and voilà you have a character revenge arc set up.

You can repeat this with basically any universe, and it still feels fresh if you just keep changing a few things around.

Did it happen recently to this person or a long time ago? Maybe change it to be a different family member or a friend. Maybe this was a massacre where there are multiple survivors seeking revenge. Maybe instead of seeking revenge they are really just trying to hide because whatever villain took their loved ones is hunting for them still.

Hell you can even push the entire thing into the past, turn the revenge arc into the lore of the world if the completion of that revenge arc would have had a large impact. Then the main quest could be trying to undo what has been done, or trying to stop another group from trying to undo what has been done. You could even obscure the actual events and make legends that all are loosely based around the truth but contradict each other so your characters need to uncover what really happened. (Cultures like having myths that make them seem better than they actually were)

When you need random characters to play roles in the plot, its often fun to just pick a random race/culture/class in your world and then say “how could a person from this group have ended up where I need them to be and with the skills I need them to have?”