Teodor Gösta Theselius, Swedish music arranger, composer, and jazz musician (piano, clarinet, and tenor saxophone). Born June 22, 1922 in Stockholm, died January 24, 1976 in the same city.

Theselius, nicknamed ”Tesse”, was a prominent organizer of jazz and pop music, who wrote and arranged for the Thore Ehrling and Sam Samson orchestras.

Highly respected by colleagues, Theselius was considered one of Sweden's foremost jazz composers and arrangers.