Ernst Stueckelberg

However, Richard Feynman did take at least one aspect very seriously, the mathematical equivalence of antimatter as time-reversed matter.

In fact, it was Swiss physicist Ernst Stuckelberg who first proposed this idea in the 1930s.

But Wheeler's one electron universe idea inspired Feynman to build this representation of antimatter into his path integral formulation and the following spacetime interpretation of quantum mechanics.

which won him the 1965 Nobel Prize in Physics.