Albus

Way too many to count. Dumbledore, Snape, Draco.. it can also depend on which book you're talking about.

Hagrid Probably!

The Giant Squid living in the Great Lake

Voldemort’s mother...

^Well, technically yes.

Dumbledore, Molly Weasley, McGonagall

Dumbledore

Honestly either Hagrid or Dumbledore!

Every character is important if your franchise isn’t trash.