Tom
Tom, like Chapman, is one of the more well-known Controllers. As Jake's brother,
Jake had to confront him every day, listen to him talk about The Sharing as if it were a
4H club, and exchange words with their own hidden meanings, while not betraying his
knowledge of who Tom really was or hinting at his own identity. Though in looking at him,
we see that we know virtually nothing of him, the actual human being named Tom who is
Jake's brother. So to analyze him, we must also look at the various entities which have
manipulated him throughout his time of being, instead of Jake's older brother, The Enemy.
Tom used to be an ordinary kid, playing basketball and going out with friends. He was very close to his younger brother, Jake, and the two of them were friends as well as siblings. But, after a while, he joined the Sharing. Even though he apparently didn't have much use for a social group like that with his basketball and everything, he joined anyway because a girl he liked was in it -- she was an "advanced member." One meeting he snuck away from the group to go see her, but in the process stumbled on a secret -- that The Sharing was an alien front. He saw Visser Three in his Andalite form. After that, unless he was killed, there was no way he could escape Yeerk infestation. He became a Controller.
The Yeerk who took over Tom (later identified as Temrash) moved up in rank very quickly. He went from being just an average subordinate to an extremely high position, just short of being a sub-visser. He was getting ready to change hosts, to the extremely important position of infesting the governor, who was running for the President of the United States. He was in a miniature Yeerk pool, awaiting his new host. But then came the Animorphs. They sabotaged the hospital operation, and overheated the Yeerk pool. Unfortunately, Jake was plunged in, and Temrash somehow was lucky (at least for the time being) enough to infest him. Thus he found the secret of the Animorphs. But it didn't last long --- the other Animorphs found out and confined him for the necessary three-day period, and Temrash died, leaving Jake with the memories of how Tom had become entrapped in the first place. It was a great blow to the Yeerks, but it probably didn't mean all that much to Tom --- he was just given as a host to someone else.
The next major conflict involving Tom came when Jake's great-grandfather died and the family had to go out of town for four days, his father wasn't going to let him be exempt. For the Controller to remain alive, he had to make his father into a Controller -- or kill him. After a few unsuccessful attempts at the former, they had to do away with Jake's dad, and it was only because of the Animorph's intervention that kept Tom from killing his father with his own hands, though they also gave him a trip to the hospital, saving the Yeerk who controlled him. So, while the situation was contained, they were back to square one.
Though who knows if Tom will ever come out of this alive. And, if he does, will he manage to keep his mind and senses intact?