Raditz!!

 

   

Goku's biological brother.  He comes to earth at the very beginning of the Saiya-jin saga in search of his brother, Kakarot.  He fails to find him, but using his scouter, he detects the 2 strongest power levels on the planet (which isn't difficult because there are very few high power levels on earth).  One must be Kakarot, first he comes across Piccolo, who is the 2nd strongest next to Goku, He fights Piccolo and proves that he is much stronger than him, he does not continue to fight because he decides that Piccolo is not a threat, and he is NOT Kakarot.  He then goes to where he saw the other power level.  Finding Goku, and failing to convince Goku to join him and destroy the inhabitants of earth, Raditz kidnaps Gohan and sets Goku a ransom of the bodies of 100 earthlings to prove himself, he will then be given his son back and another chance to join him.  He has a power level of 1,200, which at this point is higher than anyone else up until this point in the series.  Piccolo then appears and agrees to team up with Goku to beat Raditz and retrieve Gohan.  It takes a combination of Piccolo's strongest attack (special beam cannon), and a noble sacrifice by Goku do finally beat Raditz, who just before he dies, he calls another two, much stronger Saiyans (Vegeta and Nappa), who he says are now on their way to earth.  Not a nice guy.