Zell is that character who is incredibly energetic, loud, somewhat obnoxious, and friendly regardless of whether or not you want him to be. He always tries to make friends with every person he meets, with varying degrees of success. To those who don't know him well, he is a trouble maker - always on the run from the Disciplinary Committee and the Garden Faculty for breaking the rules in some way or another - riding his Turbo Board around the premises, fighting with people who tease him (Seifer in particular), and running in the hallways, as examples. Very few people see that he is actually a great guy.
He is fiercely loyal to his friends and his personal honor code and will not hesitate to prove this loyalty - as witnessed by the player when he takes the brunt of the abuse from the guards in the D-District Prison to protect Selphie and Quistis. Another example of how much he values his friendships is when he is part of a surprise plan to celebrate Squall becoming commander. He even holds Seifer to some regard as a friend, getting upset when Seifer is announced a rogue and is order to die.
Zell is quick to express his opinions, thoughts, feelings, and knowledge with the group, regardless of whether or not what he has to say will be useful or beneficial. He is proud and will never back down from any kind of confrontation, but he also knows when to defer to orders. He is a soldier, after all is said, and will do as he is ordered no matter what.