Raised by a single mother in Stuttgart, Germany, Koch initially wanted to become a musician before a chance encounter at a local theater production changed his mind. After graduating from acting school in 1985, the young actor appeared in numerous local productions before transitioning to TV with supporting roles in crime series such as "Tatort" and "A Case for Two" (1981-). His back-to-back performances in 2001 as Baader, the notorious namesake leader of the militant Baader-Meinhof Gang, and Oetker, son of wealthy German industrialist Rudolf Oetker, proved a pivotal moment for the young actor; he garnered two Grimme Awards in the same year, a first for the prestigious German TV awards body.The following years brought acclaim from both home and abroad; Koch used his French fluency to memorable effect in the star-studded cable movie "Napoléon," and turned in an award-winning performance in "Operation Valkyrie" (2004) as Claus von Stauffenberg, Hitler's luckless would-be assassin. His small-screen efforts didn't go unnoticed, and in 2006 Koch landed major feature film roles as SS officer Ludwig Muntze in "Black Book" (where he began a long-term relationship with co-star Carice van Houten); and as playwright Georg Dryman in "The Lives of Others," a chilling account of East German politics that went on to win an Oscar for Best Foreign Film. After a long hiatus from the stage, Koch returned to the theater in 2006 with a role in Oscar Wilde's "An Ideal Husband," which explored familiar themes of blackmail, corruption and fear of exposure. Koch next appeared in "God Loves Caviar" (2011) as Greek-pirate-turned-caviar-magnate Ioannis Varvakis, and was later cast opposite Bruce Willis as a villainous Russian political prisoner in the widely panned sequel "A Good Day to Die Hard" (2013).