Johan Frederik Steffensen
Johan Frederik Steffensen was a Danish mathematician, statistician, and actuary who did research in the fields of calculus of finite differences and interpolation. He was professor of actuarial science at the University of Copenhagen from 1923 to 1943. Steffensen's inequality and Steffensen's method are named after him. He was an Invited Speaker at the 1912 International Congress of Mathematicians in Cambridge, England and at the 1924 ICM in Toronto.