Grandpa Gohan is Son
Goku's adoptive grandfather. He is a master of material arts, and teaches
Goku karate, as well as the Janken fighting pose. He is killed by
Goku after transforming at the full moon, though he does not find out about this until later in the Saiyan saga.
When
Goku first landed on Earth, his mission was to, in time, destroy the entire human race and sell the planet to another race. Being a Saiyan, who are known to be very aggressive and short-tempered,
Goku was very violent and unnaturally strong. Eventually his attitude completely changes after surviving a near-fatal plunge down a deep ravine.
Grandpa Gohan makes his second appearance during the Fortuneteller
Baba saga, as the fifth fighter. He makes his final appearance at the end of dragonball where
Goku and Chi-Chi are trying to repair the magical furnace that
set the Ox-King's castle ablaze.
Read more: DBZ Son Goku Chi-Chi Yamcha Yajirobe King Piccolo Piccolo Krillin
Goku's son
Gohan is named after his Grandpa Gohan only because the baby went without a name for a while, until the name "Gohan" came into conversation, and the baby laughed because he liked the name, so they Chi-Chi,
Goku, and the Ox-King decided to name him that.