Dimitri was born in North London on March 17, 1974 to Greek immigrant parents, and formerly served as a soldier in the Royal Marines and laterly in the SBS, but left in unknown circumstances. He consequently joined MI5 as their Piracy and Terrorism Case Officer. His first mission saw him face off Somali terrorists, who hijacked a vessel with the intention of bombing the Houses of Parliament in London. The attack was stopped by the detonation of an EMP bomb beneath London. Following this, Dimitri serves as a field operative, assisting on numerous missions, frequently as armed backup. Over the course of his employment, he forms a bond with his superior, Lucas North (Richard Armitage), responsible for the integration of both Dimitri and Beth Bailey (Sophia Myles) into the team.
In Episode 4, Chinese intelligence plant a van full of explosives in a busy London street. Dimitri consequently goes there, and heroically risks his life, evacuating the area and then defusing the bomb.
Dimitri is shown to be a courageous and heroic agent, as well as an excellent spy. His approach to spying is described as 'more relaxed than Lucas', and he is depicted as a friendly and open character, who is 'consistently brilliant at his job', but 'just likes to enjoy himself.' He looks upon Lucas as a friend and mentor, and has a good relationship with other members of the team, particularly Beth, with whom he shares the experience of being new to the job. In his personal file, Dimitri is described as determined, energetic, fearless and instinctive. He specialises in piracy and counter-terrorism.
In the tenth series, Dimitri is a lot more experienced and has a much stronger voice in the team. He has a very close relationship to the new Section Chief Erin Watts. She affectionatly calls him 'D'. He was also the one to whom she turned for comfort after her daughter was used as part of a terrorist plot against London. They are also shown holding hands and embracing after Ruth's death. He also shows an extremely strong loyalty to Harry even when the team leader decides to go behind the rules to figure out who had ordered the attacks against the MI5 and Ilya Gavrik.