What inspired One Piece?
Eiichiro Oda has named his two poles precisely. To Viz, he described growing up on the anime Vicke the Little Viking, about a boy who dreams of becoming a Viking: "I feel like it's awesome to have friends on your team, just like in the 'Vicke' series." Researching pirates for One Piece, he added, taught him that Vikings were pirates too, and the crew-as-family shape of his story comes straight from that childhood favourite.
The other pole is the manga he grew up reading. In a Jump interview, Oda went all the way: "By far the manga that inspired me the most was Dragon Ball... if there was no Dragon Ball, there would be no One Piece." Luffy's traits are deliberately mirrored from Goku: the appetite, the instinct, the grin in front of the impossible.
A Viking cartoon supplied the crew. Dragon Ball supplied the captain.
WHERE IT STARTED
Weekly Shonen Jump 1997 No.34