Freeza
Freeza is the most evil underlord of them all. He went to the planet Namek to force the inhabitants to give up their dragonballs so he can wish for immortality. However, along the way he found out that his former employee Vegeta plus Gohan and Krillin were out for the dragonballs too. As it turns out, he doesn't get the dragonballs and is willing to make sure whoever did pays dearly.
In his first form, he battles against Vegeta but the match is a real stalemate.
After being taunted he transforms to his second form (war form) making Vegeta no match for him. He then stabbed Krillin in the stomach with one of the horns on his head because he was angry after Gohan shot him down. Then Piccolo, wished back with the dragonballs and fused with Nail, steps up to take a hit at him. Freeza once again gets beat but, he still has more tricks up his sleeve.
Piccolo continues to beat Freeza until he transforms again into his third form (alien form) and totally beats the crap out of him. Seeing that the newly healed Vegeta looks stronger and claims to be a "super saiyan", Freeza makes his final transformation and decides to battle him.
It appears that Vegeta is stronger but he is still no match and quickly dies. When Goku shows up, their long, tedious fight begins and the end result is that Goku IS a super saiyan and kills Freeza but not before he blows up the planet.
One year later Freeza ventures to Earth to seek revenge after being made into a cyborg by his father, King Kold. Its not long though before he meets a permanent fate after a mysterious youth, a super saiyan, named Trunks ventures from the future and cuts the competition in half...literally.
Fourth form of Freeza