How did Goku and Piccolo become friends?

I think it starts right at the Budokai tenkaichi. At the end of the fight, Goku gives Piccolo a senzu, and claims him to be a “rival”, rather than the Demon king who killed his friend. read more

) nature showing up, and Piccolo too considered Goku his rival. read more

When he is revived, he has had a bit more time to settle into his personality, and this basically becomes the Piccolo of the rest of the series. During Freeza he's indifferent to Goku, then befriends him properly when training for the Androids. read more

After Goku decided not to kill him, Piccolo’s opinion of Goku changed and they became rivals. During the team up against Raditz, they were rivals. After Piccolo killed Goku, he felt a feeling of emptiness as his opinion of him changed. read more