The Green Termite
Harry is Ben's Granddad and also The Green Termite.
He retired from the superhero life when he broke the superhero code and chose to save his family instead.
When Ben finds the insignia he seeks out Harry to get some answers.
Harry decides he can't leave his grandson to fight evil alone and even though he might be getting on a bit he's not too old to kick a bit of bad guy butt!
Not to mention the years of valuable experience he has to share to this group of young superheroes.