The librarian at Kamar-Taj, then the Sorcerer Supreme, and the only person in the catalogue who acquired the most senior magical office in the world by default.
Wong is the straight man of the magical side of this catalogue and the reason it holds together. He is the person who knows what the books say, which in a story about people improvising with forces they do not understand is the most useful thing anybody can be.
He also gets the office. When Stephen Strange spends five years dead, the position of Sorcerer Supreme passes to Wong, and the films play the awkwardness of that with unusual restraint: nobody is bitter, and nobody offers it back.