1. His owner's name is Jon Arbuckle. Jon is a cartoonist.
2. The real cartoonist name is Jim Davis.
3. The first ever strip was drawn on 19 June 1978. Thus, Garfield's birthday is 19 June.
4. Odie, Jon's dog, was actually owned by Lyman Johnson, a friend of Jon's who was his roommate.
5. Odie was first introduced in 8 August 1978 strip, along with Lyman.
6. Garfield's favorite teddy bear is named Pooky. His first appearance was on 23 October 1978.
7. Jon met his girlfriend, Liz, when he took Garfield for a checkup on 26 June 1978. Obviously, she's a vet. After so many rejections, Jon finally gets a date with Liz on 21 April 1980
8. Garfiel LOVES coffee.. and is pretty much addicted to caffeine.
9. Garfield was born 5 pounds 6 ounces, in Mama Leoni's Italian Restaurant. That explains his love for lasagna..
10. And, oh yeah, Garfield has a grandpa.
11. Garfield has an archenemy named Nermal. He's the "world's cutest kitten" owned by Jon's mom.
12. Since Jon has a girlfriend, Garfield doesn't want to be left behind too. He's been seeing a pink/purple cat called Arlene since 17 December 1980.
13. Despite his penchant for holding a newspaper while drinking coffee in the morning, Garfield cannot read.
14. Garfield has an invisible friend called Clive. He was debuted on 22 April 1996 and last seen on 16 June 2003.
If you're a big fan of this chubby cat, the full list of Garfield comics can be read here.
If you're a bigger fan, every information about Garfield is available in Garfield Wiki.