Steinbeck is a young man with an average height and build, with short blonde hair and blue eyes. He wears a flat cap on top of his head, a white shirt with his sleeves pulled up a bit, a blue overall with a black belt, and dark boots. He carries with himself a raw potato and a navaja, a tool he uses in order to activate his ability.
Steinbeck appears to be a relaxed and easygoing man, casually commenting about the countryside and talking with his partner, Howard Phillips Lovecraft, without minding being heard. His ability grants him great confidence in himself, enough to spend time talking to his enemies, which can also be his downfall.
He claims to hate chores, trying to save himself some trouble while doing them, which demonstrates that he is a cunning person. Nevertheless, he is in no way a lazy person, as he is capable enough to carry the missions given to him. Although he may be polite and kind, he shows no regard for his enemies, claiming to not care about what he has to do to them. At the same time, he is not an entirely bad person, driven by motivation of doing his job for his family.
Steinbeck's ability, The Grapes of Wrath (怒りの葡萄, Ikari no Budō?) allows Steinbeck to grow grapevines from any part of his body. By grafting the vines attached to his body to other plants, the flora in the entire vicinity becomes an extension of his body.
His own branches, as well as the others from the flora, can be used as a means to capture and hold a person or object with tremendous strength, as well as shield him from attacks.
He can even combine his ability with Q's, due to the fact that Q's ability is cursing people who hurt them. Fitzgerald's emergency plan involved both of their abilities: Steinbeck using his Grapes of Wrath to connect the plants directly into Q's body, affecting their sense of touch. Thus, when a person harms a plant in any way, it hurts Q, causing the person to get cursed.
Prior to joining the Guild, Steinbeck was a farmer in North America. It is implied that his large family was poor during such time.
Though he is one of the Guild's members, he hates Fitzgerald due to his endless ambition and arrogance.
- (to Q) "Well, some people have money and power, some people sob in pain under the ground, and some people are ordered to torture little children. But that's how it is. That's the dirty logic adults use." 
- (to Q) "You were in pain because you were born as yourself. As long as you were born with that ability, this was the only way it could have played out. There is a God out there, but I'm afraid He doesn't love you." 
- He made an appearance in the mobile game "Kimito Lead Puzzle 18" as a stage boss and a limited-time character.
- The name of his siblings is based on the actual characters from The Grapes of Wrath.
- He seems to like eating potatoes.
- John is actually good at making impressions.
- Much like Tanizaki, he cherishes his own little sister quite a lot, constantly spoiling her.
- Steinbeck is formerly a farmer before joining the Guild similar to Tom Joad, the main character from the real-life John Steinbeck's The Grapes of Wrath.