Mavic Chen was the Guardian of the Solar System who had allied himself with the Daleks in the Doctor Who serial, The Daleks' Master Plan.
Allied with the Daleks, Chen was able to supply the Daleks with the core for their Time Destructor, a full emm of Taranium, only found on the planet Uranus. However, the Taranium core was stolen by the Doctor at the Galactic Council's meeting on Kembel, who was at the time disguising himself as Zephon, Master of the Fifth Galaxy.
Much of the rest of the serial involves the Daleks and Mavic Chen chasing the Doctor and his friends throughout time and space. Eventually, Mavic Chen and the Daleks retrieve the Taranium from the Doctor in Ancient Egypt.
However, back on Kembel, the Daleks betray Mavic Chen and the rest of the Galactic Council locking them up in a detention cell in the abandoned city. Willing to destroy the Daleks, the Doctor's friends Sara Kingdom and Steven Taylor let the council out and leave the planet in their ships. Chen, however, is not so willing and still believes that he is the Daleks' allies. At gunpoint, he takes Sara and Steven to the Dalek Supreme. The Dalek Supreme then personally confirms to Chen that their alliance is at an end. Quite mad by then, Chen claimed he was first ruler of the universe and immortal, then escaped into some corridors but was soon exterminated by some Daleks.