Thomas, who grew up in the southern Frankenjura, was introduced to climbing as a child by his father and began climbing regularly with a kids group when he was 10. At 12 he started competing and came 6th in the German Lead Championship when he was 15. At 16 he climbed his first 8a sport route and subsequently realised that competitions no longer motivated him. After school he moved to Erlangen for university and began to discover his full potential outdoors.
Forced to balance climbing with studying for a duel degree in physics and astrophysics—and later a Ph.D. in astrophysics—Thomas chose to climb for the joy of the sport, rather than chasing hard routes. Nevertheless, he steadily consolidated his grades, amassing an impressive tally of 8a to 8c sport routes and hard boulder problems, some highlights of which were flashing the bouldery 8b route Ramadan in March 2013 during a trip to Suirana, climbing his first 8c, Klondike Cat in the Frankenjura, and climbing four 8A boulders (Walker on Earth, Miss Schweiz, Arête With a Pocket and Teamwork) and an 8A+ boulder (Freak Brothers) during a three-day trip to Ticino, Italy, in early 2015.