Pat Petersen, one of the top marathoners in the U.S. in the 1980s, died from complications due to pancreatic cancer early Sunday at the age of 56.

Petersen was known as one of the most tenacious runners of his time, someone who always raced to his fitness or beyond. Although largely unsung in American running annals because he never made an Olympic team, Petersen cranked out some very strong efforts at the New York City Marathon in the 1980s. In fact, he placed among the top 4 in the five-borough race three times—4th in 1984 (2:16:35), 3rd in 1985 (2:12:59) and 4th in 1987 (2:12:03). The only other Americans to pull off that feat are Bill Rodgers, Alberto Salazar and Meb Keflezighi.

Petersen wasn’t a star in high school and was known for his wonky, inefficient mechanics, but he was a runner who pushed himself to his limits while training at Manhattan College and as a post-collegiate runner working full-time as a financial analyst on Long Island.

In his debut marathon in New York in 1983, he ran 2:12:06 and placed 12th.

“He was just plain tough. He chased people. He had a higher pain tolerance than anyone else,” said Tracy Sundlun, co-founder of the Rock ‘n’ Roll Marathon Series and Senior Vice President of Events at Competitor Group who coached Petersen during the 1980s in New York City.He put himself into a well in every marathon. He went that far into it every race, unlike almost any runner ever did. He got everything out of his body every time he ran a race.”

Although he dropped out of the 1988 U.S. Olympic Trials Marathon in New Jersey, Petersen was remarkably consistent as a marathoner. In addition to his success in New York, he was equally impressive at the London Marathon, placing 6th (1985, 2:11:23), 4th (1986, 2:12:56) and 7th (1989, 2:10:04)—the latter of which was considered the U.S. best time for a record-legal course until Jerry Lawson broke it with a 2:09:35 at the Chicago Marathon in 1997. Petersen’s PR still ranks him at No. 17 on the all-time U.S. list.

RELATED: The Top 25 All-Time U.S. Marathon Times

Petersen was sponsored by adidas for part of his career and he represented Warren Street Social and Athletic Club in New York for almost a decade. He ran a 4:04 mile and ran his 5,000-meter PR of 13:42 indoors on a banked track at the New Jersey Meadowlands.

“He was old-school as you could get,” Sundlun said. “When he ran 2:10:04 in London, he worked all day on Friday and got on a plane for London, showed up for the athlete press event, ran 2:10 the next day and got on a plane for New York and was at work on Monday morning.”

In 1990, doctors discovered Petersen had been suffering from heart arrhythmia. In his last New York City Marathon in 1991, Petersen ran 2:19 despite cracking a rib when he was struck by the elbow of another runner during a frenzy at the start.

“It is only people with character who achieve the ultimate success on the biggest stages, no matter what you do in life,” Sundlun said. “He always achieved to the ultimate level on the biggest stages in New York and London. Pat Petersen had character.”

Petersen ended his career working for Dowling College on Long Island. He was diagnosed with pancreatic cancer only 10 weeks ago.

Petersen is survived by his wife, Bea Petersen, a former 2:46 marathoner, and their four children, Maggie, Eric, Jack and Joy.

RELATED: New York Times’ Profile of Petersen from 1991