He's also one of the fastest men in Lincoln, Neb.
But unless you're an aficionado of land speed racing or have lived in his north Lincoln neighborhood, where he routinely parked his incredibly fast cars outside his house, you may not know or have heard of him.
His skills at building powerful engines and driving fast cars have made him one of his sport's most respected and well known participants. And last fall, it landed him in the Nebraska Auto Racing Hall of Fame.
Watch the races
Bonneville National Speed Week continues through Aug. 15. To see live streaming of the races on the Bonneville Salt Flats in Utah, visit scta-bni.org.
His cars have set nearly 30 land speed records at Utah's famed Bonneville Salt Flats, including one driven by legendary drag racer "Big Daddy" Don Garlits. Using $20,000 Garlits gave him, Thomssen designed the rat-shaped black speedster to "go around" a Ford engine Thomssen "threw together out of spare parts," including old cast pistons and a crankshaft he pulled out of a junkyard. Lincoln auto racing great and 2007 Nebraska Hall of Fame inductee Jim Schuman built the car.
In 1988, Garlits drove the "Swamp Rat" into Bonneville's prestigious 200 mph club.
"[That engine] did indeed get Garlits into the 200-mile-per-hour club, and that's how I got famous," Thomssen says.
He's been interested in going fast ever since his father, Bill, used to take him to circle track races when he was a kid.
Married in 1958, Thomssen spent his honeymoon at drag races in Grand Island.
Not long after that, he and his college buddy Arly Asch built a drag racer of their own. The "Hayseed Special" came together in a hog shed on Asch's farm.
The body was a 1923 Ford roadster that Thomssen's father used to drive. Asch had an old Ford engine.
Thomssen admitted they had no clue as to what they were doing.
"We read the rule book and followed the rules," he says. "That was the extent of what we knew. But we did know something about the engine. Arly had already been driving it as a street roadster, a classic hot rod. We knew it went fast."
They rebuilt the engine in the basement of Thomssen's apartment.
The car enjoyed its test run in 1961 at a national championship in Indianapolis. The duo worked on it right up to its first race.
"Our first pass was against the national record holder, and, lo and behold, we beat him," Thomssen says. "We came out of it the champion."
The trophy still sits in Thomssen's living room.
"We started out calling the car the Hog Shed Special," Thomssen recalls. "But the more we thought about it, well, we were just a couple of hayseeds and nobody had ever heard of us. Nobody had ever seen us. We decided we'll just call it the Hayseed Special. It represented more of the Nebraska flavor."
"The whole epitome of racing in the early days when I was in college was to set a land speed record in Bonneville. Car magazines always featured all these Bonneville cars. That was a big deal. By the early '60s, drag racing became more prominent, but
Bonneville was still there."
In 1978, Thomssen's car called the "Goldenrod" ran more than 186 mph at Bonneville, resulting in the first of Thomssen's 29 Bonneville records. All but one has been broken since.
Bonneville National Speed Week is Saturday through Aug. 15, and Thomssen will be there crewing for his grandson-in-law, Ryan Krejci. Krejci now drives the Hayseed Special, that first car Thomssen raced until 1967 before parking it in a field of weeds. Thomssen brought it out of retirement in 1997, using the chassis of the old car as a base for the new one, and has raced it since.
Thomssen gave up driving three years ago, but has no plans to stop tinkering with engines anytime soon.
"It's something that I can do," Thomssen says. "Most anybody who is successful at something will tell you that."