Grandpa Gohan (aka Gohan the First) is the adopted grandfather to Goku. He is voiced by Lanipator. So far, he only appears in the special Bardock: Father of Goku.
Trivia[]
Him being voiced by Lanipator (voice of Vegeta) may be a reference to FUNimation dub, as Chris Sabat voices both Vegeta and Grandpa Gohan
He makes reference to Clark Kent (aka Superman) since Toriyama based the Z origin of Goku on Superman. (Specialy in DB- and Dragon Ball Super: Broly, where Bardock and Gine didn't sent him to Earth to conquer it but instead to survive)
In Freeza Burn, Goku makes a reference to his grandpa, saying he doesn't need a bath (after pulling back by Piccolo from the lake).