Dylan Klebold was an American high school senior from Lakewood, Colorado. He and his schoolmate Eric Harris were responsible for the Columbine High School massacre (1999). His psychological profile suggests that Klebold was "an angry depressive, who showed low self-esteem, anxiousness and a vengeful attitude toward individuals who he believed had mistreated him". He had not been diagnosed prior to his death.

In September 1981, Klebold was born in in Lakewood, Colorado. Lakewood is a home rule municipality (self-governing settlement), and one of the most populous cities in Colorado. In 1980, it had a population of about 114,000 people. Klebold's parents named him after the Welsh poet Dylan Thomas (1914 -1953).

Klebold's parents were the engineer Thomas Klebold and his wife Sue Klebold (née Yassenoff, 1949-). Thomas initially worked as a sculptor, but found engineering to be a more lucrative profession. Sue worked in assistance services for the disabled, though she later changed her career to caring for people with brain diseases. Through his mother, Klebold was a great-grandson of multimillionaire Leo Yassenoff (1893-1971). Both parents were Lutheran, though Sue came from a Jewish family.

Klebold was raised in a religious household, and "attended confirmation classes in accordance with the Lutheran tradition." He spend the fist two classes of elementary school in Normandy Elementary School , and was then transferred to Governor's Ranch Elementary School . He was considered "exceptionally bright" as a child, and joined a program for students with "high intellectual potential". He was also interested in sports, regularly playing baseball, soccer and T-ball. During his elementary school years, Klebold was a Cub Scout.

After graduating from elementary school, Klebold enrolled at Ken Caryl Middle School. He reportedly found the transition to a new school difficult. Klebold was thought to be painfully shy, and rarely opened up to people. During his middle school years. Klebold befriended Eric Harris, who was a few months older than him. During Klebold's high school years. Harris became his best friend.