Jack

A man of very large stature. Jack is kind, compassionate, and insanely intelligent. However, he usually lacks confidence and won't acknowledge his qualities. He will do his best to help you with all your troubles and will even do your homework for you if you ask nicely. He is particularly knowledgeable when it comes to science, and may even be on the autism spectrum. If you have a Jack in your friend group, you have a friend for life, a lovable teddy bear and an intimidating bodyguard all rolled up into one.

Dave: Oh man, I'm really struggling with this science homework.
Josh: Sounds like you need a Jack in your life.