Mark Dennis was born in 1970 in Portsmouth, Virginia to Nancy J. Dennis. He graduated from Vandalia-Butler High School and from Wright State University with a degree in Chemistry.
Mark was employed as a Chemist at Isotec, Inc. in Miamisburg, Ohio for 17 years where he was recognized as Employee of the Year. He had a strong interest in astronomy and science fiction from an early age. He also enjoyed making home repairs, gardening and exercise. Mark excelled at so much in life: In fact, he has been described as a "Great Son, a Great Friend, and a Great Chemist." It was his wish to use Celestis' Memorial Spaceflight services.
He was preceded in death by his maternal grandfather Jack E. Tritle and uncle, Byron C. Hall. He is survived by his mother Nancy Dennis of Miamisburg, Ohio, aunt Constance Hall Simpson (John) of Dayton, Ohio, uncles Douglas Tritle (Margaret) of Altus, Oklahoma and Steven Tritle (Judith) of Tipp City, Ohio, and numerous cousins. Sadly, his beloved grandmother Dorothy Tritle of New Carlisle, Ohio passed away in August 2008.