Described as being a Turtle of massive size with an ancient appearence, Maturin existed long before the creation of the mainstream universe in Stephen King's novels. By nature, Maturin is kind and benevolent, having a very grandfather-like demeanor when speaking to humans. Maturin is said to be constantly withdrawn into his shell, sleeping, rarely ever coming out for anything. One of the occassions in which he did come out of his shell was when he had a stomachache which caused him to vomit out the mainstream universe, after which he promptly retreated back into his shell. Because of this, It, a creature that existed in the void within the Macroverse and an adversary of Maturin, considered the turtle to be old, lazy, and stupid. However, given his vast amount of wisdom, power, and the aid he has provided to those in need of it, It's perception of the turtle seems to be false.
In It, Maturin seems to serve largely as a spectator of the events that unfold in the battle between It and the Loser's Club, only involving himself to advise the young Bill Denbrough during the Ritual of Chüd in 1958, while Gan provided them with most of their strength.
The name Maturin itself is a reference to Stephen Maturin, a naturalist from the Aubrey–Maturin series of novels, written by Patrick O'Brian, who discovers a new species of tortoise which is subsequently named for him.