|The Big Bang Theory Staff|
|Birthday||December 21st, 1983|
|First Episode||The Staircase Implementation|
|Number of Episodes||1|
|All of the Big Bang Theory Staff|
Yeun was born in South Korea, and shortly after, he moved with his parents to Troy, Michigan, where they owned two beauty supply stores. Yeun received a bachelor's degree in Psychology from Kalamazoo College in 2005, but during his freshman year, he'd gotten into acting. Following his graduation, Yeun moved to Los Angeles, California, to pursue an acting career, and received several minor roles over the years (including voice roles), but did not get his break until AMC's hit series The Walking Dead, which began in 2010, and has recently completed its fourth season. Yeun's character Glenn in The Walking Dead is a former pizza delivery boy, and is valued for his navigational skills. Yeun got the role mainly due to his incredible physical likeness to Glenn from the comic series of the same name, in which the television series is mainly based off of.
Yeun only appears for a moment in the episode "The Staircase Implementation". His name is not stated, but was given in the credits as "Sebastian". Sebastian is the first character from the Building of whom Leonard meets, and warns Leonard to "run away, dude", when Leonard goes to the apartment building in response to an add for a roommate placed by Sheldon. Sebastian's intolerance toward Sheldon's behavior becomes apparent when Leonard enters Sebastian's former room to the phrase "DIE SHELDON, DIE" written on the wall in red paint. Sebastian was suggested to have had a scientific background of some sort, being that it was Sheldon's standard for a roommate. It is unknown if Sebastian and Sheldon had gotten the apartment together, or if he had come in before or after Sheldon had moved there.