Emperor Zurg

Emperor Zurg (also known as Evil Emperor Zurg or simply Zurg), The Sworn Enemy of the Galactic Alliance and the arch enemy of Buzz Lightyear, is the tertiary antagonist in Toy Story 2. He makes a cameo appearance in Toy Story 3.

Toy Story
Zurg does actually appear in the first Toy Story. As he introduces himself to the toys, Buzz describes his "occupation" as a member of an elite universal protection unit to protect the galaxy from Zurg. Later, when Buzz and Woody argue at a gas station, Buzz mentions about Zurg building a secret weapon with enough power to destroy an entire planet, making a reference to the Death Star from Star Wars Episode IV: A New Hope. Andy also mentions Zurg when he plays with Buzz on his birthday. His appearance is only shown in one of Andy's drawings, although his head is obscured by another drawing.

Toy Story 2
Zurg appears in two forms in Toy Story 2. The first form appears during the opening sequence, where he is initially seen tracking Buzz's location through his fortress inside his control room. A little later, he is seen doing battle with Buzz, in which Zurg, using his portal gun, blasts the top half of Buzz's foot into smithereens; however, the opening sequence is revealed to be only a comic book.

Much later in the film, an incarnation of Zurg is later accidentally released by Andy's Buzz Lightyear in Al's Toy Barn. Believing himself to be real much like Andy's Buzz has done in the first film, he pursues after Andy's Buzz to destroy him. He seems to have followed Andy's Buzz across the street, through an air vent of Al's apartment, and up the elevator shaft as he is seen arriving atop the elevator when Andy's Buzz and his rescue squad of toys head back to the elevator after Al packs Woody and the Roundup gang into his case and leaves his room to head for the airport. Along with the group is another Buzz Lightyear action figure (also released from Al's Toy Barn by Andy's Buzz Lightyear), who also believes himself to be real. Both Buzz #2 and Rex, a fan of the video game "Buzz Lightyear: Attack on Zurg", are caught with surprise by Zurg's unexpected arrival. A showdown occurs between the Buzz #2 and Zurg atop an elevator, where Zurg uses his chief weapon (which appears to be a Nerf ball gun.) During this battle, after overpowering the other Buzz, Zurg reveals he is Buzz's father (a parody of the duel between Darth Vader and Luke Skywalker from Star Wars Episode V: The Empire Strikes Back). As Zurg sets his gun to his highest level and is about to finish Buzz #2 off (at point-blank range), Rex, not bearing to watch the duel anymore, turns away, but his large thick tail hits Zurg, knocking him down the elevator shaft. While Rex finally feels excited about finally overcoming his frustration toward not being able to defeat Zurg previously, Buzz #2 suddenly feels forlorn about losing his father. Zurg seems to have survived the fall as he, with one of his horns slightly bent backwards, is seen playing catch and spending "quality time" with Buzz #2 when Andy's Buzz and his rescue squad make their way out of Al's apartment. The Buzz #2 describes Zurg as a "great dad" as he rushes to catch another ball fired by Zurg.

Zurg's name is mentioned once again by Andy (after he returns home from Cowboy Camp to see Jessie and Bullseye added into his collection) as a polecat who has stolen his space cows.

Toy Story 3
Zurg is mentioned again by Buzz, who sees Andy's toys as minions of Zurg after Lotso turns him back to his original settings, which is one of the indicators to Andy's toys that Buzz thinks he's a space ranger again.

At the end of the film, when Andy introduces Buzz to Bonnie, Andy mentions Zurg, from whom Buzz is sworn to protect the galaxy from. Zurg makes a brief appearance in the end credits of Toy Story 3, where he is shown being donated to Sunnyside Daycare in a box along with a dinosaur, a giraffe plush, and two Fisher-Price Little People. He is helped down to the floor by Stretch and meets Ken and Barbie, who welcome him to a now cool and groovy Sunnyside, of which the two are leaders. He is later seen doing the robot dance.

It was revealed on Lee Unkrich's now defunct Formspring that this was a different Zurg than the one in Toy Story 2.

Toy Description
From Official Website:

"The ultimate force of evil in the galaxy, terrifying tyrant Emperor Zurg is unswerving in his quest to destroy his enemy, Buzz Lightyear."

Trivia

 * Zurg appears as a playable character exclusive to the PlayStation 3 version of Toy Story 3: The Video Game, along with his custom-made car.
 * Zurg appears in the Buzz Lightyear Astro Blaster Level in Disneyland Kinect Adventures.
 * While Zurg and Buzz #2 fight atop the elevator, as the talk button of Buzz #2 is repeatedly hit, it skips the message "Buzz... Buzz... Buzz Lightyear to the rescue," which also happens when Woody and Buzz fight underneath Andy's car at the gas station in Toy Story.
 * When looking at the shot where Zurg is about to finish the Buzz #2 off, it is noticeable that the levels on his gun are numbered to 11, a reference to Nigel Tufnel's amplifier in This is Spinal Tap.
 * Zurg's character may appear to draw from Darth Vader, a main villain in the Star Wars original trilogy, with a similar voice, appearance, and set of mannerisms.
 * A fun meal miniature figure of Zurg appeared in the Toy Story Toons episode, Small Fry.
 * Zurg was actually to have a slightly bigger role in Toy Story 3, according to the original script. He was one of the recalled toys along with Buzz Lightyear. A quite insane Zurg was the first one to introduce Buzz to his ultimate fate of not being repaired, but sent to the toy crusher. Much easier to just ship out a new one, than actually repair the recalled toys.
 * The character may also be based on Emperor Ming in the 1980 film Flash Gordon, because he sports a cape similar to that of Ming's and is referred to as "Emperor".
 * During Woody's nightmare earlier in the film, some of the the mismatched toy arms in the trash can Woody was discarded in belonged to Zurg (although there were a couple color variations).
 * Zurg was based partially off Toy Story 3 director Lee Unkrich's favorite toy, the Six Million Dollar Man.
 * The "Zerg" faction in the Blizzard produced computer game Starcraft originally had their name spelled identically to Emperor Zurg's during the game's earlier builds. However, in order to avoid possible copyright issues, the faction later had it's name re-spelled with an "e" instead of a "u."
 * According to concept art, Zurg is really just a small alien in robtic armor.
 * In the Buzz Lightyear of Star Command intro, Zurg is seen in Andy's room that possibly means that Andy might've had a Zurg toy or borrowed one from a friend at one time. However, it is unknown what happened with it, but most likely it was donated, given back (if it was indeed just borrowed), sold, or thrown away during the events between Toy Story 2 and Toy Story 3. It is also unknown what relationship he had with Buzz. On the other hand, however, this may just be non-cannon.
 * In the Buzz Lightyear episode The Lightyear Factor, Zurg enters an alternate universe where he finds an Evil Buzz Lightyear ruling the galaxy. The Zurg from that universe was a burger guy at Cosmo's restaurant, not having what it took to be Ultimate Evil.
 * Buzz #2 spending "quality time" with Zurg may possibly be a reference to Kevin Costner's character Ray Kinsella reunited and playing catch with his father in the final scene of "Field of Dreams."
 * In World of Cars Online Zurg has a cameo where he is depicted as a train in an arcade game.