3-D

3-D is one of the guys in Biff Tannen's gang back in 1955 along with Match and Skinhead. His nickname comes from the distinctive character trait that he is always wearing a pair of 3-D glasses (a reference to the 3-D movies that were popular in the 1950s).

Back to the Future
He is there with Biff and the others when Biff shows up to bully George McFly about doing his homework at Lou's Cafe, and when Biff nearly starts a fight with George's son, Marty McFly from 1985 (who passes himself off as a new student named Calvin Klein), and then later when Marty does manage to start a fight with Biff at Lou's Cafe. After punching Biff, Marty runs outside, knocking Match, Skinhead, and 3-D down on the way. When Marty tries to escape on a make-shift skateboard, the gang chases after him in Biff's car. A brief chase ensues, ending with Biff's car crashing into a manure truck, causing the car and the bullies to end up covered in manure.

The three are with Biff at the "Enchantment Under the Sea dance" to get back at Marty, who had brought Lorraine Baines as a "date." While Biff tried to have his way with Lorraine, he tells them to take Marty around back so he could deal with him later. The three carry Marty over to a car and lock him in the trunk. Unfortunately for them, the car happens to belong to the band playing at the dance: Marvin Berry and the Starlighters, who promptly chase the bullies off and free Marty.

Back to the Future II
3-D and the others still work for Biff in the alternate 1985 serving as his security (this is the only timeline in which he is seen after 1955). The three knock out Marty when they find him out in front of Biff's hotel, and take him upstairs. They later chase Marty through the hotel after he confronts Biff about the almanac, though Marty manages to lose them. In this timeline, 3-D trades his 3-D glasses for a pair of tacky novelty sunglasses albeit with red and blue lenses, similar to 3-D glasses.

The younger 3-D also manage to cause trouble for Marty when he returns to 1955 to get the almanac back and restore the timeline. After Marty manages to take the almanac off of Biff at the dance, the bullies chase him through the school. Although Marty loses them, the bullies spot Marty's "other" self performing onstage at the dance. They correctly assume it's the same person (though they wonder how he managed to change clothes so fast), and they get ready to jump him when he gets offstage. To protect his other self, Marty climbs up into the rafters and drops a set of sandbags on them, knocking them out.

Trivia

 * He is portrayed by the actor Casey Siemaszko.
 * He along with Match and Skinhead's nicknames are only given in the films' novels, screenplays, and credits.