As a child, Oda was inspired by vikings and aspired to become a mangaartist. At the age of 17, he submitted his work "Wanted!" and won several awards, including second place in the coveted Tezuka Award. That got him into a job at the Weekly Shonen Jump magazine, where he originally worked as assistant to Shinobu Kaitani's series Suizan Police Gang before moving to Masaya Tokuhiro on Jungle King Tar-chan and Mizu no Tomodachi Kappaman, which gave him an unexpected influence on his artistic style. At the age of 19, he worked as an assistant to Nobuhiro Watsuki on Rurouni Kenshin, before winning the Hop Step Award for new artists. During this time, he drew two pirate-themed one-shot stories, called "Romance Dawn", which would debut in Monthly and Weekly Jump in late 1996-early 1997. In 1997, One Piece appeared for the first time in Weekly Shonen Jump and promptly became one of the most popular manga in Japan. His biggest influence is Akira Toriyama, creator of Dragon Ball and Dr. Slump. They have also made a one-shot called Cross Epoch, a crossover containing characters from both Dragon Ball and One Piece.
Eiichiro Oda was one of the assistants of Nobuhiro Watsuki, along with Hiroyuki Takei. Therefore, Oda has a strong respect for Takei. 1
In Rurouni Kenshin, you can see the Straw Hat crew's pirate logo on one of the bombs made by Gein, most likely drawn by Eiichiro Oda when he was the assistant working with Nobuhiro Watsuki.
Eiichiro Oda is married to Chiaki Inaba, who had played Nami during Jump FestaOne Piece stage performances.
He voiced the character "Odacchi" in a soccer-themed short that aired with the 3rd One Piece Movie. "Odacchi" is Oda's nickname, and he played soccer when he was younger.
According to Oda in an interview for US Shonen Jump, his favorite villain in One Piece is Buggy the Clown (he joked that he literally threw him together).
One trait that Oda is renowned for is inserting easter eggs in his One Piece manga for fans to spot such. In the past, these have included the character Pandaman and the logo Doskoi Panda.
According to Mike McFarland on the commentary track for episode 17 of One Piece, Eiichiro Oda himself has given his solemn approval of FUNimation's uncut dub of the series.