David Forster Jr. could run fast, but sometimes he just wanted to get others across the finish line.

That’s why the 2:37 marathon runner throttled down his 6-minute pace to run alongside his fiancée in Grandma’s Marathon earlier in June, helping her finish her first 26.2-mile race. A week later, the 27-year-old elite runner collapsed and died blocks from his Minneapolis house as he finished an 8-mile evening run.

His death has numbed a running community from ­Hopkins High School to St. John’s University, where he graduated in 2011.

“We all know we’re going to die some time,” St. John’s cross-country coach Tim Miles said. “But at age 27?”

Forster’s friends gathered Tuesday evening to “finish his run,” celebrating their friend and teammate along a loop he might have run June 24, the night he collapsed, said fellow runner and friend, Andy Clasen. Afterward, they planned to gather at a Minneapolis softball field to watch Forster’s team play.

Forster was a natural athlete “who always made you look twice whether it was playing basketball or making a one-handed grab on the football field or running,” said Clasen, who was one of three friends Forster helped coach through last fall’s Portland Marathon. “I think he would have carried us across the finish line if he had to.”

In college, Forster was one of the top runners on the cross-country team and excelled at track and field, competing in the physically demanding steeplechase event in which runners jump 35 barriers, including a water pit.

“He never ever got both feet wet,” Clasen said. “He was really very good at it.”

Unlike some athletes, Forster arrived at St. John’s, a Division III school, and took it seriously, said friend and teammate Justin Rose. He was competitive and always wanted to do his best, becoming a silent leader among his teammates, Rose said.

“He didn’t talk a big game. He walked the walk. … I was never as fast as him, but it was fun to watch him. … He was so competent and good at what he did, but he never made anyone feel bad about themselves because he was better than they were.”

Those who knew him said Forster had a magnetic personality that brought people together, connecting different groups of friends, whether it was on the playing field, on a 10-mile training run through the woods or a dash to Chipotle. He was as passionate about the Green Bay Packers as he was about music.

“He was always at the center of the group without even trying,” said former teammate and friend Dustin Franta. “He had a charisma that was open and relaxed.”

His entrepreneurial spirit evolved from a lawn-care company he started in middle school to a mini-athletic shoe empire he grew in high school.

“He was really into shoes, especially basketball shoes,” said high school and college friend Alex Ruble. “Whenever they released new shoes he would wait outside Champs Sports, standing out there in the cold until they opened. He would buy whatever he could, sell some online and then keep a pair for himself.”

After college, where he studied global business leadership, Forster worked as an analyst for Target Corp. Four years later, he left to work with his mother at her growing company, little pepper promotions.

For the past few days, Rose and Forster’s family and friends have been coming to grips with how the dreams of an athlete and aspiring businessman have been cut short.

“Being as young as we are, our natural first response was: Why? How?” Franta said.

His parents, Sandy and David Sr., are taking comfort that their son was the happiest he’s ever been because he fell in love four years ago and planned to marry his fiancée, Abby Hansen on New Year’s Eve in Duluth.

It all seemed picture-perfect, they said. “He went at his happiest.”