In Death Fanlisting

From wikipedia:
First Appearance: Naked in Death
Eve's third victim is the owner of a cat; Eve takes the cat into custody. However, the victim's daughter is too distraught to take the cat, and Eve has it at her apartment, trying to find a name for it,when the perpetrator of the book has Eve at gunpoint, the cat brushes past his leg, distracting him and giving Eve the leverage she needs to fight back. Eve thus names the cat Galahad, after the Arthurian Knight, because he was her knight in shining armor.

The cat is Eve's, Roarke's, and Summerset's pet; he is often fed by all of them and takes food as he pleases, and occasionally steals it. On occasion, Eve has had bad dreams from which she wakes up to find Galahad trying to wake and comfort her. On other occasions when Eve falls dead asleep Galahad sits on her butt. When Nixie, the title character from Survivor in Death, stays at their home, she stays mostly with Galahad, as he comforts her. When Mavis brings Belle for a visit Creation in Death Galahad is scared of the baby.

Eve mentions later in Memory in Death that the cat has been neutered. The cat makes minor appearances in almost every book.
He is described as a fat heavy and lazy gray cat with dual colored eyes, one green and one gold.