In the late 1950s, Tappert started taking part in movie and television productions. His big breakthrough was in 1966 with the three-part television show "Die Gentlemen bitten zur Kasse", in which he played train robber Michael Donegan. In 1968, he changed sides by playing Scotland Yard detective Perkins in Edgar Wallace movies. When the second public television station in Germany, the ZDF, started planning a new mystery series with a different type of investigator in 1973, he was chosen for the character of detective Stephan Derrick, with sidekick assistant Harry Klein (played by Fritz Wepper).