Tyrell is known for his fearlessness and poor sense of danger, as well as for his pride and curiosity. He is established as being a bit of a troublemaker, and his latest incident was the cause of the hunt for the Roc's Feather. Tyrell's impulsiveness means that he sometimes accepts and creates unnecessary challenges, such as challenging Blados immediately after fending off an ambush. He also has a bit of a temper, which does lead to problems during the quest.
Despite all this, he is extremely loyal to his friends, and openly states his opinion that he doesn't deserve friends as good as Matthew and Karis. In addition, he is very honest and down to earth: which is why Matthew is "proud to call him his best friend", as brought up in the encyclopedia, and demonstrated by his rather blunt remark in front of Paithos (who surprisingly doesn't chastise him for this). Over the course of their quest, Tyrell does appear to mature a bit, and his loyalty and courage begin to show. It is implied that he can be insightful at times, despite his impulsiveness. For example, he realizes the trap that King Wo is about to trigger, and is the first to notice that Ryu Kou was not a native of Te Rya. Just before the Apollo Lens is set off, he is the only Adept to realize that Sveta is reading his mind, and wishes her luck.