On the left is a picture of Walter Koenig as Leo in the 'Ironside' episode "The Summer Soldier". On the right is Herve Villechaize as Tattoo in 'Fantasy Island'.
I'd say they could be brothers in Toobworld. Or is it just the meds talking?
It's not like we learned that much about the life of Tattoo during the run of the series. We barely got to learn anything about Mr. Roarke - only that he was over 300 years old and had supernatural connections with mermaids and Satan. (With the added information... information... information from the remake, Toobworld Central stands by its theory that Mr. Roarke was a Gallifreyan Time Lord.)
An added benefit to this "Theory of Relateeveety" is that we never learned the last names of either Leo or Tattoo.......