Dennis Lappin is a firefighter from Michigan who first competed in Denver in American Ninja Warrior 6, he winded up suffering an injury on the second obstacle, the Cat Grab. While jumping to the first wall, his right leg hit the wall very hard, resulting a ruptured Achilles. Although he was able to clear the obstacle, he later failed the next obstacle, Spinning Log, and needed six months to recover from his injury.
Dennis returned to compete in Kansas City in American Ninja Warrior 7, he became the first competitor to finish the qualifying course, he placed 29th and moved on to the city finals, in the city finals, Dennis failed the Body Prop but placed 15th and advanced to the national finals for the first time. His run on Stage One was cut but it was revealed that he failed the very first obstacle, Piston Road.
In American Ninja Warrior 8, he was not called back to compete. It is likely he was one of the many veterans not called back.
After not getting called back for the previous season, Dennis returned to compete in Kansas City again in American Ninja Warrior 9. In qualifying, his run was digested but it was shown that he finished the course, placing 10th. His run was digested again in the city finals, but it was shown that he failed the third obstacle, the Broken Pipes, which took out many competitors.
Dennis was not selected to compete in American Ninja Warrior 10, but he tested the courses in Indianapolis and Philadelphia.
Once again, in American Ninja Warrior 11, he was not called to compete. He tried to walk on in Cincinnati, but was not selected. He did however, get a chance to run the course as a tester.