Dylan Bennet Klebold was born on September 11, 1981, in Lakewood, Colorado. His parents, Thomas and Sue Klebold, had met while studying art at Ohio State University and got married in 1971. They had another son, Byron, who was born in 1978. Shortly after Dylan was born, he faced a health issue called pyloric stenosis, which caused severe vomiting during his early months.

As a child, Dylan was described as intelligent but somewhat sheltered. He attended Normandy Elementary School for first and second grade before transferring to Governor's Ranch Elementary School. There, he participated in a program for gifted children and showed promise in his studies. However, when he moved to Ken Caryl Middle School, he struggled to adjust and was often described as painfully shy, especially around new people and women.

Dylan enjoyed sports and was involved in activities like baseball and soccer. He joined Cub Scouts and made friends with Brooks Brown, who lived nearby. During middle school, he met Eric Harris, who would become his closest friend. Their friendship grew, and they formed a tight-knit group of friends that included Nathan Dykeman.

Both boys were later employed at Blackjack Pizza, where they worked as cooks. They shared interests in computers and video games, particularly the game Doom. While Eric was known for being more outgoing and charismatic, Dylan’s shyness remained a significant part of his personality. Reports indicate that in their last year of high school, Dylan began to show signs of anger and frustration, which contrasted with the more reserved nature he had in earlier years.

Dylan attended Columbine High School, where he participated in various school productions and helped with computer tasks. While some accounts suggest that he and Eric were targets of bullying, others indicate that they had a close circle of friends and were not outcasts. They wore trench coats as part of their style but were later mistakenly associated with a group called the "Trenchcoat Mafia," which was not accurate.

In the years leading up to a tragic event, Dylan kept journals and created videos that reflected his feelings of isolation and yearning for acceptance. He attended his high school prom three days before the event that would forever mark his life and the lives of many others.

On April 20, 1999, Dylan Klebold and Eric Harris carried out a deadly attack at Columbine High School in Columbine, Colorado. They arrived at the school shortly before noon. The two boys had prepared for the attack by gathering firearms and explosives. They had planned to first detonate two propane bombs they had left in the school cafeteria, intending to shoot the students who would flee after the explosion.

At 11:19 AM, after arriving separately, they began their assault. Klebold went to a different entrance than Harris and both carried out their plan. They left duffel bags containing bombs in the cafeteria and set out to start their attack. Since the bombs failed to detonate, they resorted to shooting students and staff members with their firearms.

Klebold and Harris targeted fellow students as they moved through the school. Witnesses reported seeing them fire at classmates and throw bombs. During the rampage, 12 students and one teacher were killed, and 24 others were wounded. The attack was chaotic, with many students trying to escape and hide.

After completing their attack within the school, Klebold and Harris returned to the library, where they held several hostages but did not harm them. They had ample ammunition and could have caused more destruction. Instead, after a short while, they exited the library and began shooting at police outside.

Shortly after 12:08 PM, they took their own lives. Harris shot himself in the mouth with a shotgun, while Klebold used a TEC-9 handgun to shoot himself in the temple. Their actions left a lasting impact, as this incident became one of the deadliest school shootings in United States history.