TK-421/Legends

TK-421 was the designation of one of the stormtroopers who was guarding the Millennium Falcon while captured in Death Star I. He and his counterpart TK-422 were summoned up the ramp and were incapacitated by the crew and/or passengers of the freighter. His stormtrooper armor was then taken by Luke Skywalker and used to sneak through the Death Star.

An addtional search of the Millennium Falcon was ordered after it was discovered that a group of Rebels had infiltrated the detention block where Princess Leia Organa was being held. The search party discovered TK-421 and TK-422 both tied up in a service locker, stripped of their armor, and unconscious. All initial attempts at reviving the two comatose stormtroopers failed. They were then taken to the nearest hospital bay. It is likely that TK-421 died aboard the Death Star when it was destroyed.

Behind the scenes
In the novelization of the movie, the trooper was referred to as THX-1138, in an homage to George Lucas' first feature film.

It is speculated that TK refers to the type of trooper, and 421 is the serial number for troopers of that type.

TK-421 was the only stormtrooper to receive a designation in any of the three original trilogy movies.

TK-421 has become an easter egg of sorts mentioned in various places such as the movie Boogie Nights.

In the video game Jedi Knight II: Jedi Outcast, a homage to TK-421 is included. In the Cairn Installation stage, the player will eventually enter a control room marked by six trip-mines in the entryway. If he moves towards a static-filled screen, he can hear a British-accented human speak:

TK-664, what is your status? TK-664, report!

In the same game in multiplayer the name "TK-421" is used for the Stormtrooper outfit, too.