Bill Stewart (ビル・スチュワート, Biru Suchuwāto), occasionally referred as Bill Martin is a semi-recurring character in Hajime no Ippo.
When WBA featherweight super champion Ricardo Martinez was to go against Japanese boxer Date Eiji a second time in his 18th title defence, Bill arrived with Ricardo to Tokyo. Bill went with Ricardo to the Otowa gym for a public sparring session that included the JBC featherweight champion Makunouchi Ippo. When it was Ippo's turn to spar, Bill instructed Ricardo to handle the spar however he liked, but to show the audience the difference between Japan and the world. After Ricardo effortlessly hits Ippo with lefts and stops his Dempsey Roll, Ricardo walked away and told Bill who then explained the reporters that Ricardo has no intention of destroying the pride of the Japanese champion, simply wanting to warm-up his left, and any more than that would be pointless. After the spar, Bill commented how surprised he was to see someone in Japan able to use the Dempsey Roll and that the Japanese champion had a good amount of power, wondering if Ricardo felt a chill down his spine before apologising for asking a "stupid" question since he believed no matter who Ricardo fights or what they use, Ricardo has no reason to feel agitated. Later, Bill attended the press conference between Ricardo and Date.
When Ricardo's 18th title defence match against Date arrived, Bill was his cornerman for the match. Prior to the match, Bill told Ricardo he won't give him a strategy, asking to destroy him with technique and experience, and to show the people of Japan the true magnificence of boxing. After the first round, Bill noticed that Date had levelled up since the last time, but since Ricardo had as well, Bill instructed him to prove the strength difference had not changed in the second round. After the second round, Bill believed that Date probably had experience against fighters with very strong punches, with the experience being the reason that he was brought this far. After the eighth round, Ricardo wondered why Date still stood after taking so many punches. Bill replied to have confidence in his punches, believing that Date probably reached his limits, but he felt that Date has miraculous toughness, as if he has something that holds him up past his physical limits, like the dream to become world champion or revenge against Ricardo, however Ricardo disagreed. After Ricardo blocked Date's Heart Break Shot, breaking Date's fist in the ninth round, Bill wondered if they still planned to fight, deeming it foolish for his second to allow him to continue. The match continued into the tenth round where Ricardo downed Date and won the match by knockout, defending his title for the 18th time.
Bill was Ricardo's second when he fought an American in his 21st WBA featherweight title defence, winning and defending his title in the first round by knockout.
Alfredo Gonzales called Ricardo to get him to reconsidered a rematch between them. He mentions if he beats Ippo, he wants Ricardo to accept his challenge. Except, Ricardo doesn't remember who Ippo was.
Alfredo mentions that he heard that Ricardo sparred with him when he fought Date. However, Ricardo mentions that he has sparred with countless men, where his opponents maybe one thing, but he can't remember every single person he has sparred with, where he doesn't remember Ippo's name.
After the call, Bill mentions to Ricardo that Ippo used the Dempsey Roll, where Ricardo finally remembers who Ippo was.
Using Sendō Takeshi previous 4 matches against Mexican boxers, Bill had Jose Nargo use the "Hit and Run" tactic. He notes that Sendō's power is fearsome, but like a "Saber Tooth Tiger", it only scary if it is able to hit. He remarks the reason why his kind died out was because it was too slow to catch it's prey. Sendō is the same.
Bill has the appearance of a middle-aged man with white short hair. He wears brown tinted shades.
Bill is somewhat of a cocky and intelligent trainer, just judging by the fact that when Ricardo was going up against Date he wasn't worried much. However when Ricardo hesitated to finish Date due to the fact that an unfortunate accident could occur, he demanded that Ricardo finished him. During the Jose Nargo vs Sendō Takeshi match, Ippo comments that Bill is known for being a great tactician. He believes the perfect boxer is a combination of science and violence. He mentioned that he felt elegance and technique aren't enough to claim the world, and that there are times when savageness to coat the ring in blood is required.
- His surname was originally Bill Stewart in the anime and manga, but was changed to Bill Martin in Round 1122 for unknown reasons, unless it is his middle name rather than his surname.
- It was then changed again to Bill Stewart in Round 1275.
- Bill is able to speak at least three languages - English, Spanish, and Japanese.