During his first appearance when he assaulted the Yakuza, Gotou wore track shoes, gym shorts and a tank top. He had short brown hair, with a round face, and kept his eyes closed most of the time.
To hide from the authorities, he then changes his look to have a longer face with sharp features. He has a large muscular and toned physique, which is often covered in suits. In the anime, his second appearance seems older than his manga counterpart.
Towards the end of the series, Gotou transforms into a 3 meter tall monster. The outside of his body gains a gray tinge to it, and has the appearance of exposed muscle. His face becomes sharper, sporting pointed ears and a mouth full of fangs. He also has four arms and a tail of sorts, his legs become reminiscent of a dinosaurs.
Gotou is one of the more intelligent of his kind. He has shown a superiority complex over the human race, believing they are nothing but trash. He shows no remorse in combat, dismembering his opponents without a second thought. He has shown to be a patient person, waiting for his turn to attack, and even allowing Shinichi to leave, so that he may recover. Though he believes himself to be above humans, he still considers himself nothing more than an "organism." Unlike Reiko, he couldn't care less about the purpose of Parasites, saying he lives only to fight.
In his transformed state, his thoughts become more primitive, worrying solely on survival and exterminating the human race. He was also more aggressive and became easily angered in this state, something that played a part in his downfall.
As a parasite, Gotou has the basic abilities to shapeshift his head, and maximize the physical potential of the body he's controlling. he can harden his cells for offensive and defensive purposes.
Gotou's body consists of five individual parasites, and has complete control over each one. He is able to maximize the powers of each parasite, shapeshifting and utilizing them to his every whim. He has shown the knowledge of transforming his legs into a state, that allows him to easily run beside a truck speeding along the highway. While in the woods he morphs in lower legs into prongs that allow him to cling and jump through trees, becoming more agile than a monkey (stated by Migi).
His defense capabilities are far beyond that of a normal parasite. By having the parasites in each of his appendages harden themselves, he is able to fend of powerful shotgun blasts at close range, leaving only minor dents in his skin (holes in the anime). He has also created a shield using his forearm, by expanding and harding it. Though the shield was more of a demonstration, as he was left unscathed, from a direct hit from a grenade launcher.
Gotou has shown to be exceptionally dangerous in close quarters combat, by using his enhanced speed, he was able to kill dozens of armoured and weaponed soldiers in seconds.