In case you didn't know there's this iceberg:
The first one is Garfield minus Garfield A lot of people know about this comic, it's centered around Jon Arbuckle and and most of the panels he's talking to himself and showing to be really depressed I don't know why people would make the comic but it represents how alone and sad Jon really feels without Garfield distracting us from it
Garfield and Friends is a Garfield show with silly plots and storys most people know about it
The Garfield show is similar it's one of the more recent Garfield shows with Garfield in silly plots not much to say about it
Garfield: his nine lives is a comic, and a TV special that shows us Garfield's past lives and his future one!
(Level 2)
Square root of minus Garfield is Garfield comic strips with altered plots
Heathcliff controversy: heath was before Garfield technically but if you include the Jon comic (it's really similar to the Garfield comic except about Jon) it would be technically before heathcliff heathcliff is a other orange cat with shows music and such that also eats a lot
Lyman is the owner of Odie he was in the early Garfield comics until he suddenly disappeared and in a question book there's a couple of answers of what may have happened to Wyman and in The Garfield show there's another explanation but the creepiest one in the answering book is don't look in jons basement and in one of the Halloween garfield games Lyman is in his basement!
Garfield is dead theory is centered around a comic around Halloween as well it's a really creepy comic but Davis has confirmed it's not in the actual Canon and it was just to freak people out so the theory is not true
Garfield's scary scavenger Hunt is a Halloween game and I said earlier in this game Lyman is in the basement and I'm not sure if it's the sequel or in the first one lyman's head is in the stove later,
Diana's piano: and one of the past lives Garfield had he was a kitten named Diana who lived a long happy life until Diana died on the piano that her owner played for her
Jon Arbuckle is a cartoonist: Jon was originally supposed to be a reflection of Davis but he grew into his own character a very pathetic but his own character he is still a cartoonist in the Canon
(Level 3)
Garfield's mom and grandfather: there's been a couple instances where Garfield's mom has been shown or his relatives Garfield was born in the Italian restaurants and his first food was lasagna
Arlene is a stray: I'm surprised not more people know about this but Arlene is a stray there has been some instances where it's been hinted at in the comics
Lab animal: one of Garfield's past lives was a lab animal he was injected with some sort of fluid and scientists were going to dissect him but he ran away and soon turned into a dog and pretended to be one of the search dogs for the rest of his life before being reborn
Lyman is in jons basement: I explained this one earlier I don't need to come back to it
Garfield's exact weight: not many people know this but Garfield's exact weight is 40 lb!
Big Bob come: in the comics it was spelled weirdly because that's how the caveman would say it but it wasn't spelled the most brilliant it said "big Bob cum"
Nermals owner: in the debut comic of nermal it said that Jons mom is the owner of nermal
(I'm going to do the rest soon but this is a lot to cover so I'ma stop right here and to make a sequel)