Arlene

From Garfield Wiki

Arlene is Garfield's on-and-off girlfriend. A thin pink cat who seems to be the only one living thing in the world who can successfully crack jokes at Garfield on a regular basis. She has distinctively big lips and a very thin neck. Earlier in the series she also had a gap between her teeth; she also appeared more often than now. She first appeared on December 17, 1980. Although she never appeared on the animated series (with the exception of a cameo appearance in the fourth season), she appeared in the film version as well.

In the book Garfield's Judgement Day, it was revealed she was a stray cat, which she had never revealed to Garfield until emergency situations brought it to light.