Dennis was born in Chicago, Illinois, on May 6, 1939, to Theodore and Valerie Schmidtke. In 1957, Dennis graduated from Arbor Vitae High School, Woodruff, Wisconsin. His accomplishments include lettering in football, baseball, and basketball. An impressive achievement was when Schmidtke scored 52 points during the Northern Lakes Basketball Conference. Final game score: 95-46.
Dennis obtained a Bachelor of Art in History and English at the University of Wisconsin-Stevens Point, in 1961. While continuing to excel in sports at the college level, Dennis earned varsity letters in both football and basketball. As a freshman, he was the school's starting quarterback, and was named Outstanding Freshman Athlete of the year.
From 1961 to 1966, Schmidtke taught History and English at Antigo High School, Antigo, Wisconsin. In 1967, he earned his Master's in Counseling at the University of Alabama, Tuscaloosa, Alabama. He served as a guidance counselor at Antigo High School from 1967 to 1995.
As a member of the Antigo Red Robin's Football coaching staff for 26 years, Schmidtke served as Varsity Assistant Backfield Coach for the last 22 years of his career. He helped establish the Red Robins as an enduring power known for their outstanding running game. During his tenure as Backfield Coach, the Red Robins won 3 Wisconsin State Championships, 13 Wisconsin Valley Championships, and had 7 undefeated teams! Schmidtke also coached the Antigo Red Robin Varsity Golf Team from 1986-1995.
Upon Schmidtke's retirement from coaching and education, he received a certificate of honor from the General Assembly, Senator Kincaid, and Representative Ourada, acknowledging him on behalf of the people of Wisconsin for his dedicated years of service, and the pride he brought to the Antigo community.