What are Thomas's character traits in The Maze Runner?

Thomas, from “The Maze Runner,” is a somewhat naive, but intelligent and curious individual. To be fair, most anyone would be naive in his situation—stripped of his memories and placed into a mysterious glade in the center of a maze with other adolescent boys.
Thomas, however, is defined by his courage and his upright nature, as well as his intellect and curiosity. He is always willing to stick up for other boys in the group, and he willingly goes into the maze to help find and save another boy from the vicious creatures that reside there.
He is also a willing and capable leader, around whom the other boys rally and to whom they look to for guidance. His courage and care for the others make him a very good leader.

How does Thomas develop throughout The Maze Runner?

During the course of The Maze Runner, Thomas grows as an individual and develops relationships within the difficult social situation into which he is thrust. At the outset, it is clear that Thomas’s memories of his personal life have almost vanished. He strives constantly to remember that prior life and to make sense of the confusing new environment that he shares with the other adolescents confined to the Glade and the Maze around it.

From being a newcomer, Thomas develops close friendships and soon takes on a leadership role. He shows courage and tries to help his comrades even when it can get him into trouble. As Thomas becomes increasingly fearless, he chooses to become a Runner. His courage is shown when he endures a Griever’s sting as a method to recover a key memory—one that turns out to be essential to their escape. Although many of the children escape, others pay with their lives. Thomas feels the emotional pain of grief for those who perished in the escape and helped save his life.

Among the other captive children he befriends, Theresa is especially important. Thomas’s growing empathy is shown when she is jailed and he realizes he is powerless to help her. He even contemplates stealing the keys to the cell and letting her out:

[H]e didn’t want to leave. He almost wished he could get thrown in the Slammer with her …

Thomas felt an incredible sadness. He wanted to steal Newt’s keys and help her escape.

Thomas’s growth is also shown by his willingness to take dangerous actions despite his fear. He promises the others to get them home. Before he becomes a Runner, he accompanies Minho and the other Runners for an expanded exploration of the Maze. As they prepare to depart, he tries to conquer his nerves:

Butterflies swarmed in his gut, and he just wanted to move, to quit thinking about it. After all, going out in the Maze was no worse than staying in the Glade with open doors …

A sudden urge gripped him. “Don’t forget my promise!” he yelled. “I’ll get you home!”

What are Thomas's ethics in the book "The Maze Runner"?

In ‘The Maze Runner,’ the character Thomas is presented as curious but fairly uncomplicated, quiet but doing his own thing and going his own way quite subtly but innocently. He has his own sense of ethics, his own inner ‘moral compass’ to guide him. He is also persistent, almost dogged, in his pursuit of answers and he doesn’t give up so he exhibits the character trait of perseverance. He is honest and direct when trying to make sense of his surroundings:

‘all I want is some help.’

This persistence can come across as constant moaning however, and we see his confusion when his curiosity is not addressed. The Maze is an enigma to him - a puzzle he has almost become obsessed by - and he develops a one track mind about it. He simply has to become a runner so he can satisfy his curiosity and solve the riddle. As readers we empathise with him, feeling his shock and loneliness at suddenly being in a weird new world - and also feel his frustration as he tries to make sense of it. In order to do this - and make his mind up for himself - he becomes a bit of a ‘doubting Thomas’ reminding us of the disciple in the Bible who tested everything, even the statements Jesus made. Thomas doesn’t take answers at face value, he tries them out. He is also a creative thinker and he doesn’t allow set ways of thinking to cramp his style - he sees the whole picture instead of being hide-bound by rules and boundaries. His own sense of ethics directs him to follow his inner compass and to do the right thing instead of following the example of the other boys. Sometimes he finds this difficult and we discover that he is brave and can hold his nerve to stare out another boy. Then there are other little conquests, until subtly - through his own brand of ethics in seeking the truth - Thomas emerges as the leader.