I rewatched an episode from the original Outer Limits series that starred Martin Landau. He played Andro, a man in the future who encounters an Astronaut from the 1960s played by Karl Held. Back in the 20th century, a man manipulated bacteria from outer space. It mutated and infected the entire human race, causing horrible changes in the appearance, and impacted reproduction. The astronaut and Andro attempt to go back in time to prevent the disaster.
I was curious and did some research on Held. A few years after the Outer Linits episode, Held appeared in an episode of the original Star Trek (Return of the Archons - 1967).
Ten years later, Held went full circle, acting opposite Martin Landau again in an episode of Space 1999 (The Immunity Syndrome 1977).