Evil Roy

For some reason, writers seem to like to use the name "Roy" or "Leroy" to name a less than lovable character - ether as an out and out villian or as the Butt Monkey of the story. This is perhaps because the name comes from the word "Royal", and therefore could sound like the name of a privileged person who needs to be taken down a peg or two.

Named for Evil Roy Slade, a tv movie about a wanted outlaw.

Examples of Evil Roy include:

Comic Books

A short-lived comic series starring Mr. T features our favorite fool-fightin' ass-kicker taking on a villain with the very imaginative name of Stare Roy.

Films

A Very Brady Sequel: 'Roy Martin' is an alias used by the bad guy.
- Although it should be pointed out that only the name 'Martin' was canon from the Brady Bunch pilot refering to her as Carol Martin. The Sequel writers decided to call him 'Roy'.
Roy Batty from Blade Runner, although it's hardly clear that Roy Batty is evil, so this may be an aversion, or, from a certain point of view, a subversion.
In Primal Fear, the suspect in a horrific murder has a split personality. Aaron is innocent, and Roy is the violent killer. Roy is also the only real personality. He made "Aaron" up to get away with murder.

Literature

In The Kane Chronicles Carter names the Set Animal 'Leroy'.
The owner of the model ship Lillian B. Womrath was named Leroy in the original book version of Stuart Little.
In Rosalie Hale's Backstory in Twilight, she was raped and abused by Royce King.

Live-Action TV

Emergency: Subverted with hero Roy Desoto, although he does tend to take a back seat to fellow paramedic John Gage.
Evil Roy Slade: The Trope Namer
One episode of Mash featured an annoying visiting surgeon from the 8063rd named Roy who was traded to the 4077th for Hawkeye.
McHales Navy: Capt Binghamton's assistant Lt Leroy Carpenter, making him the Butt Monkey's Butt Monkey.
Subverted with NCIS, with its protangonist Leroy Jethro Gibbs. Or maybe not, considering how he prefers Jethro over Leroy.
The Office: Pam's fiance and Jim's rival.
Wings

Music

Bad, Bad, Leroy Brown

New Media

Leeeeeeeeeroy Jenkins!

Newspaper Comics

U.S. Acres and Roy the Rooster.
Garfield used Evil Roy Gato as a persona. ('Gato' means cat in Spanish, incidentally).

Video Games

Leeroy Jenkins!
Roy Koopa from the Super Mario franchise.

Web Comics

Averted with Roy from Order of the Stick, who is the leader of the adventuring party and a fairly nice guy.

Western Animation

Subverted with Roy from the U.S. Acres segments on Garfield and Friends. He may be a Jerkass who delights in pranking the other farm animals, but he still does what he can to help them out.
Leroy from the Lilo and Stitch Series Finale Leroy And Stitch is the prime epitome of this trope, as Jumba was forced to bring him back, under orders from his former science partner, Doctor Hamsterviel.
One episode of Fat Albert and the Cosby Kids featured 'Cool Roy' who liked to vandlize traffic signs.
Roy is the human version of the hated Poochie staying with The Simpsons in the episode Itchy & Scratchy & Poochie.