Krillen!!

Krillen is Goku’s best friend. They met as children and were, at first, fierce rivals, He convinced Master Roshi to train him along with Goku by bribing him with a porn magazine.  He was the 2nd youngest contestant ever to qualify for the Tenka'ichi Boudaki when he and Goku both qualified at age 12 and 13 (along with Yamcha and Master Roshi).  He is only a human, so he can never be as strong as Goku or the other characters, (I think he has a final power level of about 3,000,000, which isn't bad considering the average power level for a human is between 5 and 8!!).  At first he is one of the most powerful characters but later takes a back seat to people such as the androids and the Saiyans, but during Dragonball he does  really good job of keeping up with Goku in strength and skill, not bad considering.  He is however, (in the world of Dragonball), the strongest ‘human’ on earth, and although he his really small (like, 4ft tall), is extremely strong and a brave and talented warrior. He will always fight alongside his friends and be there for Goku when he needs him, (it is his death in the Namek saga at the hands of Frieza which pushes Goku over the edge and transforms him into a super Saiyan). During their time on Namek, Krillen also becomes firm friends with Gohan, who he protects with his life at all times.

Krillen isn't too smart, but he can be funny as heck! This is one of the reasons why he is my favorite character,  he sort of provides most of the comic relief-not only in Dragonball, but even more importantly in Dragonball Z which is based more heavily on the martial arts aspect rather than the comedy and humor which was the main focus of Dragonball.

Side note;  He never has much luck with the ladies, and can get pretty clumsy around them.  He does grow his hair back in Dragonball GT and even a moustache (believe it).   Contrary to popular belief, Krillen is not naturally bald. He shaved his hair as a monk and continued to do so after he starts training so that it can not be grabbed in battle (which is a problem for others such as Goku and Yamcha).

Also, the six dots on his forehead are not holes as has been suggested, they were burned onto his head when he was a  Shaolin monk at the Orin temple (in the early episodes when he and Goku etc were children).