Bald of Awesome: Averted—his baldness is the only thing about him that isn't awesome. He wears a hat almost all the time to hide it.
Blood Knight: He dedicates his entire life to fighting bad guys, with only two minutes of sleep each night, he's stated that he'd get bored if he became president and killed all the bad guys, and if he had a magic wand, he would use it to turn every alien in the universe evil just so he could kill them.
Heroic BSOD: Goes into one in the animated series after realizing he's murdered good guys. He only snaps out of it when the others give him "a super-secret birthday gift": the identity of who killed his parents.
Wig, Dress, Accent: Axe Cop uses a variety of disguises at his disposal. He dresses up as a cat while killing bad guys in their sleep at night, he occasionally wears a baby suit, he dresses up as Ethan for comic conventions, and he occasionally disguises himself as a regular cop (he switches his axe with a gun).
Butt Monkey: He never stops transforming. Although many of these forms make him even more powerful, he never gets to use his true form, even when he tries. Even Axe Cop has stated that his best friend is Sockarang and not Flute Cop, who has been his sidekick since the first comic.
This is averted in the animated series, where he is not only still human, but married. Dinosaur Soldier and Avocado Soldier appear in one episode, but Flute Cop returns in the next episode.
I Have Many Names: Due to his many transformations. The same character has gone by the names Flute Cop, Dinosaur Soldier, Avocado Soldier, Uni-Avocado Soldier, Ghost Cop, Drag-Tri-Ghostacops Rex, Viking Cop, Bear Cop, Zombie Bear Cop, President Zombie Bear Cop, Rat Cop...
Out of Focus: After the first arc left him a tiny biting robot, he didn't reappear until a later comic demonstrated his battle cry, which also included defunct forms of Flute Cop. An even later comic showed that he got better and is still alive.
Expy: When he first appeared on Ask Axe Cop, he showed traits very similar to Axe Cop. He even had an airborne tyrannosaur as a steed—specifically, his Bat Warthog T-Rex. These were dropped when he got his own arc.
Ascended Extra: Originally Gray Diamond was just one of several superheroes featured in the story "Bat Warthog Man Can't Find His Friend" only, but the producers of the animated adaptation loved Rob Huebel's performance so much that they made him a series regular.
Real Men Wear Pink: Before becoming a chihuahua himself, he was a tough, muscular, mustachioed army man...who owned a pet chihuahua. There's something inexplicably funny about seeing such a manly man say "Oh no! I forgot to feed my chihuahua!"
Superhero Packing Heat: Has "army powers", which essentially seems to mean the ability to use a machine gun while in chihuahua form.
Multiple Choice Past: In the comic, he is an Author Avatar of Malachai, as stated above, who directly assists Axe Cop. He is an entirely different character in the animated series, where he is an aged English scientist (the smartest man in the world, no less) whose daughter, Isabella M, was held ransom by Adolf Hitler to force him to construct a zombie army for the Nazis long before the series' present day. (It isn't made clear whether this happened during World War II or some other time other than "a long time ago".) He has since become a zombie himself, but he was turned good by her daughter, who completed his secret work on a potion to turn zombies good.
Was Once a Man: The result of Grey Diamond combining the remains of his deceased friend Sergeant G (actually Sergeant T, but Grey Diamond didn't know that) with parts from a lion, a cheetah, and a robot suit.
I Want My Beloved to Be Happy: Was willing to hide her feelings for Axe Cop so he could marry Axe Girl... thankfully though, things between Axe Cop and Axe Girl didn't work out, and things ended happily.
Who's Laughing Now?: He only became a bad guy after Axe Cop refused to let him on his team, at first because he had to go fight Psydrozon and then because he was already powerful enough to go without him.
Big Eater: Claims to have eaten all the candy in the universe—whole, as Axe Cop later recovers a thousand candies still in their wrappers.
Bond Villain Stupidity: When he has Axe Cop and Ghost Cop trapped and knocked out in his oven, Turkey Turkey leaves them there for four weeks so they can wake up on Thanksgiving day, because "I like my Thanksgiving dinner well-rested."