Syrus Truesdale is a student at Duel Academy, and Jaden's best friend and roommate in the Slifer Red dorm. He's timid, shy and emotional. He gets text anxiety and has trouble standing up for himself, but Jaden is always there to encourage him.
Syrus can't swim, which presents itself as a problem in several instances.
His lack of confidence stems from his older brother Zane, a third-year Obelisk Blue. Zane doesn't believe Syrus belongs at Duel Academy, and is brutally honest with Syrus, telling him that he's a disappointment, not knowing the difference between 'using' a card and 'playing' one.
When the souls of Duel Academy are threatened by the vampire Shadow Rider, Camula, Zane duels her and offers up his soul in exchange for his brother's, actually telling Syrus that he loves him.
Syrus, like most of the other boys at Duel Academy, has a crush on the Dark Magician Girl. When the spirits of duel monsters cross over into the real world on Duel Monsters Spirit Day, the real Dark Magician Girl shows up and duels against Jaden (though everyone watching thinks she's just another student in costume). At the end of the episode, her spirit gives Syrus a kiss on the cheek.
In season 2, Syrus moves up to Ra Yellow, but remains good friends with the Slifer Red students. He also develops a petty rivalry with Tyranno Hassleberry, as both duelists want to call themselves Jaden's best friend.
He later moves up to Obelisk Blue.
Syrus often lags behind other characters, and will usually whine "Wait up!"
Syrus: "AAAAHHH! YOU DID WHAT? So then where am I going to sleep?"
Jaden: "I'm sorry. I guess in all the excitement, I didn't think about that."
Syrus: "EXCITEMENT?! YOU TRADED MY BED FOR A CARD!!!"
Jaden: "But I got it for you! Isn't your birthday next week?"
Syrus: "IT WAS LAST TUESDAY! And I'm surprised I made it with everything you've put me through this year! I might need a NEW ROOMMATE!"
Jaden: "This is so un-chill! I sleep through one of Crowler's boring lectures and he makes us lug 14 replacement duel disks across campus! Why's everyone losing theirs anyway?"
Jaden: "Huh? You know something, don't you?"
Jaden: "Come on. Spill it."
Syrus: "I don't know for sure, but I've heard things. You know the west river, right? Over by the main bridge?"
Jaden: "Yeah. What about it?"
Syrus: "Well, there's this bully who hangs out over there. Uh, so I hear. And he forces you to duel him. Uh, so I'm told."
Jaden: "Yeah. And?"
Syrus: "And if you lose, his gang takes your duel disk away!"
Jaden: "What else do you know? Come on."
Syrus: "I'm just telling you what I heard! He might not even exist. For all I know, this guy's just a myth...the big ugly muscle-head."
Jaden: "Hey, where's your duel disk?"
Syrus: "Uh, well..."
Jaden: "Sy, did you duel this guy and lose?"
Syrus: "YES!!!! And he took my lunch money, too!"