Clyde is a massive, bald psychopath with sickly grey skin, no eyes, and his mouth hanging open, wearing a butcher's attire and toting around a huge cleaver.
For most of the game, he slowly and mindlessly lumbers around the chamber, looking for the player and completely blind. He is, however, sensitive to sound, and will immediately know where the player is and start chasing them down if they run. He will also investigate loud noises like props being thrown around. He can be stunned for less than a second if a prop is thrown at him. Getting hit three times by Clyde will result in the player's death, although his swings are slow enough that they can be dodged if the player is fast enough.
The Voice mentions that Clyde is also a cannibal, as evidenced by the countless butchered and half-eaten corpses strewn about the complex. The Voice also explains that Clyde was treated as a freakish outcast due to his imposing appearance, which led to his violent insanity as seen in the game. The only noises he makes is panting when chasing the visitor.