John Archibald Wheeler
Einstein suggested that Newtonian theory would be impossibly complex if put in covariant form, although since Einstein made that claim it has been formulated in covariant form by several physicists, including Élie Cartan in 1923 and Kurt Otto Friedrichs in 1927. Charles W. Misner, Kip Thorne, and John Archibald Wheeler, in their textbook "Gravitation" (1973) Ch. 12 present the covariant version of Newtonian theory.