Gyumaou

Gyumaou is the father of Chichi.  He trained under Kamesennin along with Son Gohan(Goku's grandfather).  He doesn't play much of a role in the series

Oolong

Oolong is a shape-shifting, communist pig.   He can only stay in a shape for a few minutes at a time.  (He got kicked out of shape-shifting school for stealing the teacher's panties.) Goku and Bulma met him when he was terrorizing a small village.  Bulma decided to drag him along, because she thought his shape-shifting power might come in handy. 

Karin-sama

Karin-sama is the white cat who lives at the top of Karin Tower.  He's many centuries old, very wise, and the keeper of the Chousui-water.  He is also the one who grows the senzu beans.

Piccolo Daimaou

Piccolo is Kami's evil half.  He managed to conquer the world, and is responsible for Kuririn, Chouzu, and Kamesennin's first deaths.  He was defeated by Goku, and is the father of Piccolo from DBZ.