Along with all of the above answers, Tenshinhan. He was Goku's first real rival that wasn't as big of a villain as say, Vegeta and Piccolo, and at the same time, was more of a serious rival to Goku than Yamcha and Krillin (which is why I considered him his first real rival). He was also the fourth strongest person in the world in the 23rd Budokai, behind only Goku, and the literal God (Kami) and the literal Devil (Piccolo).
Because of this, it's disappointing for myself, as well as many people, to see him surpassed by Krillin at the End Of Z, although this is likely because of Krillin's potential unlock by Guru on Namek. At least he has a bad ass move in the form of Shin Kikoho, which he likely developed on King Kai's planet, and that move was helpful against both Cell and Boo, where he saved #18 and #16, as well as Dende and Mister Satan.