(CNN) -- After a classmate pulled out a gun in class, Kendrick Castillo couldn't just stay still. He was surrounded by the friends he considered family and they were all in danger.
"I know that because of what he did, others are alive, and I thank God for that. I love him. And he is a hero and he always will be," his dad, John Castillo, said.
"He just loved people that much."
The 18-year-old was watching "The Princess Bride" in his British literature class when the shooter pulled out a gun, demanding that nobody moved. After Kendrick lunged at the shooter, three other students also tackled the gunman and tried to subdue him while the rest of the class fled the room.
Kendrick was an only child, but his friends, including the members of the school's robotics team, were like his siblings, his father said. They would host holiday gift exchanges at his home, shared his toys as a child and would pay for a friend's movie tickets if someone didn't have money.
"Be selfless, that's what my son was, and it got him killed, but he saved others," Castillo said.
'He was extraordinary'
Kendrick grew up speaking English and Spanish in suburban Denver and first attended Catholic school. He would also spend time fishing and camping with his late grandfather -- who had been in the Marines.
"Kendrick was proud of him, proud that his grandfather was a hero," Castillo said. "Part of me knows that Kendrick wanted to live that legacy."
The teenager had kept the flag that once draped his grandfather's casket close to him and would pray and kiss his tombstone at Fort Logan National Cemetery.
"He loved the patriotism," Castillo said. "We are Hispanic by nature but we love America to the core."
Castillo and his wife Maria were not surprised to learn that their son ran toward danger. They raised him to be responsible and "to be good."
"This wasn't your average kid," Castillo said. "He was extraordinary."
The moment they learned about their son's sacrifice
Shortly after the shooting, Castillo and his wife Maria were frantically trying to reach Kendrick on his cell phone. They initially thought their son might have been injured, but grew more concerned when he would not pick up their texts and calls.
"I was a little bit guilty, because as I was trying to call him, I thought, well, maybe this is the wrong thing? Maybe I am putting his life in jeopardy by having the phone ring," Castillo said. "My anxiety and the lump in my chest was growing."
One of Kendrick's friends sent Castillo a text saying Kendrick had rushed toward the shooter, but at the time, he didn't know what to think about it. They watched as other students exited the yellow school buses and reunited with their parents, "and we didn't have that," Castillo said.
"I couldn't believe this was happening to my son," Castillo said.
The couple learned Kendrick was killed when they went to the hospital looking for him and officials told them his body was still inside the classroom. As they waited to see their son, students would come up to them calling their son a hero.
As Castillo and his wife mourn their son, he said they wish for Kendrick's classmates to heal, go to college, get married and start their own families surrounded by love.