Calvin's best friend. Though he's always harbored a reluctance for adventure, here he's gone to straight-up running away from danger, at least until "Thunderstorm".
Beware the Nice Ones: Gets pretty steamed up to the point of nearly killing Sherman, if it wasn't for Calvin's interference in "Remember." "R.I.P Calvin" and "Thunderstorm" also shows him in a Let's Get Dangerous mode.
He started to become more of a Dirty Coward. Word of God says that this was an unintentional Flanderization, as they inadvertently made Hobbes so cowardly he was almost unlikeable. To resolve this, they took Hobbes' cowardice Up to Eleven in the Season 3 finale, until Calvin finally calls him on it with a "The Reason You Suck" Speech, prompting Hobbes to subsequently make an effort that seems to have stuck in the seasons that followed.
Dissonant Serenity: As a part of his status as Cloud Cuckoolander, he handles most of the more dangerous situations with some of the most unusual upbeat cheeriness. This is even Lampshaded during "Pranking The Ghosts" where he immediately switches back to his odd self just mere minutes after beingattackedbyaghost! Twice!
While Rupert and Earl invaded Earth, took control of every living being there, and turned it into an army base, Socrates has been napping under rubble the whole time.
Retro Chill has him calmly reading an alien field guide as Galixoid and Nebular's ship falls into the lava ocean and the two aliens and Bob are screaming in terror. Especially since he somehow knew the ships were lava proof.
Distressed Dude: Has been held hostage by Dr. Brainstorm twice for ransom (even though Calvin shows no concern for him at all) and in "Nocturnals" the mist tells him that something is after him."Black Rain" has him being kidnapped by Thunderstorm and Shadow.
An eight-year-old boy (named after his voice actor) who starts out with no personality. It doesn't take long for Character Development to kick in, making him the Only Sane Man by the third season. He's also Sherman's owner.
The Stoic: The fact that he has no qualms about the fact that Calvin lives with a tiger is only one example of how open-minded he is. In fact, Word of God has said that it's that open-mindedness that allows him to take part in Calvin's adventures.
The Smart Guy of the group, an egoistical one at that. Because of this, his status as The Friend Nobody Likes (save Andy, his owner) goes unchallenged until Season 3, where he becomes friends with Calvin. He's still not fond of Hobbes or Socrates, though.
(asking Hobbes to make him a sandwich) "Now cut the turkey thin, but not too thin. Now put the mustard on the turkey in a clockwise motion, and then place a slab of cheese on top. Pour the mayonnaise on top of that, but in a counterclockwise motion. Add an extra slice of turkey on top, and then place the second slice of bread on top, and make sure the two slices of bread are even."
Arguably the most useful of Calvin's inventions, being a Do-Anything Robot. Though he doesn't have much of a personality in Seasons 1 and 2, when he gains speech in "An MTM Episode", he finally becomes something of a proper character.
Hoist by His Own Petard: In his earliest appearances, Rupert would disguise himself whenever he'd arrive on Earth as a human criminal of the same name. (The Season 3 episode "The Five Calvins" implies this was intentional on alien!Rupert's part.) This comes back to bite him at the end of the Season 5 premiere when Calvin arranges for Rupert to be arrested by police while wearing his human disguise.
Dragon Ascendant: With Rupert's arrest in the Season Five premiere, it looks like this may be happening to Earl.
They Just Dont Get It: The only reason they believe that Calvin is the Supreme Earth Potentate is because Galaxoid and Nebular told them. They steadfastly believe this to be true, despite all evidence to the contrary (including Calvin flat out telling them).
Susie: Calvin, you live by your own rules! You make things up! You create! You destroy! You tease temptation! You do all sorts of horrible things, most of them to me, yes, but then there are days you do good all on your own! You shouldn't let something like Karma run your life! You need to be rude and nasty and gross and weird, so that you can be good on your own accord.
Belligerent Sexual Tension: While it is still downplayed like it was in the comic strip, Calvin and Susie have had the odd quasi-romantic moment.
Berserk Button: While she's harmless enough at face value, all it takes is Calvin throwing a water balloon or a snowball at her to unleash the wrath of hell upon him.
Repeat What You Just Said: Sometimes Hobbes will go off on a hypothetical romantic tangent about Calvin's supposed secret feelings for Susie. While the comic strip's Calvin would've usually started fighting him, this version of Calvin prefers the more subtle approach: "I'm sorry. What did you say?" in a dangerously low voice. Hobbes tends to shut up after that.
Motor Mouth: The Klein at the prank store listing the items the Prank Starter Kit contains in "Let Us Prank the Fool":
"Well, we have your standards. We got your whoopee cushions, we got your squirting flowers, we got your spinning bowties, we got regular ties that roll up like noise-makers, we got your trick wires, we got pies, we got joy buzzers, we got silly string, we got condiments, we got fake gum, water balloons, disguises and mustaches and roller skates and fake hands and fake thumbs and fake toes and a fake nose and wigs and exploding figs and bending twigs and fake wings and ding-a-lings and loads and tons of other things! We got yo-yo's with invisible strings! We got sunglasses with songs to sing! We got dental floss and balls to toss, action Diana Ross! We got magnets and fragments and flip flops and garden crops! We got worms in a bag! We got a suit with a tag! We have also a TV that doesn't change channels! Air conditioners stocked from air from our air conditioned air condition factory!"