Dumbly was an ENTP. His youth with Grindlewald is a lot like my current period. Perfectly willing to allow genocide in order to achieve his aims. Later in his life he is Highly creative, treats Harry like a Rook, not intimidated by Voldys INTJ, makes up stupid words and uses them in conversation quite normally.
ENTP.
Gandalf was more than likely an INTJ. Belmakor might have been an INFJ though...