Sebastian Grayle Decurion Sebastius Gralae , also known as Sebastian Grayle and " Leofric of Exeter " , was a man who made a deal with the Nimon for immortality . Repeated frustrations by the Eighth Doctor made him obsessed with killing the Time Lord . Biography . In 305 AD , the Romans had an advance fort set up to protect Roman Britain from the aggressive forces of the Picts . Amongst the soldiers was Decurion Sebastius Gralae . When his older brother claimed the family inheritance , Gralae had enlisted in the Roman Legion as a means of gaining the wealth and stature he would need to marry his beloved , Julia . When the communicator from a Nimon scout ended up in his possession , he negotiated a deal to sacrifice all the men in his fort in exchange for immortality . This would give him time to take the family inheritance from his brother . The Eighth Doctor stepped in to prevent the sacrifice of the fort ' s men , but couldn ' t stop a partial release of power — enough to make Gralae impervious to harm , and to keep him alive for centuries . Grayle found himself a changed man , with fears and doubts . He spent the next 80 years seeking forgiveness with a community of monks in the northern British Isles , watching them age and die while he was untouched by time ' s hand . He married twelve women , only to watch every one of them fade into old crones . As the centuries passed , the years weighed more heavily on him . . . and he blamed the Doctor for his misfortunes . In 1055 , the stars aligned properly for the Nimon to try again . Grayle , now going by the name " Leofric of Exeter " , had prepared for the event by building a transport capsule to the Nimon ' s design . The Nimon also taught him how and where to mine uranium and turn it into plutonium to power the capsule . Grayle staged an assault on the court of Edward the Confessor , but the Doctor ' s interference again prevented him from succeeding . By 1806 , the stars were in alignment again , and Grayle was ready . He had replenished his supply of plutonium , and rebuilt the capsule in Wycombe Caves with the help of the Hellfire Club . Once again , the Doctor appeared and managed to strip away Grayle ' s immortality , but not before Grayle succeeded in bringing the Nimon to Earth . The Doctor used his TARDIS to block the Nimon ' s travel , however , and Grayle gave chase in the Nimon capsule for a confrontation within the Time Vortex . Grayle stated that he had no children , but at Charley Pollard ' s Singapore rendezvous with Alex Grayle , he referred to Sebastian as his grandfather . ( AUDIO : " Seasons of Fear " ) Alternate realities . In one turn of events , the Eighth Doctor was thrown into the Vortex and perished . Grayle successfully handed the Earth and the TARDIS to the Nimon , who used Earth to take over all of space and time . Unsatisfied with his revenge on the Doctor , Grayle asked the Nimon to create a variant timeline where he could meet up with the Doctor in Singapore and gloat about his victory . The meeting , quite satisfying for Grayle , initially set the Doctor on his travels to stop Grayle ' s actions . In another , the Doctor travelled through the Time Vortex back to 4th century Britannia , at the Roman fort . There , the Doctor gave the original Grayle the riches he would need to marry Julia , preventing the entire course of events . The future Grayle was furious with this last attempt to stop his ascension to power . The past Gralae , horrified by what he might become , killed the future Grayle and then thanked the Doctor for his kindness . ( AUDIO : " Seasons of Fear " ) Personality . Grayle was initially a pious man , with a firm belief in Mithras . However , after his contact with the Nimon , his belief and support shifted to them . As he progressed past a thousand years of age , Grayle became more distant from people and much more coarse in attitude . Eventually , he lost all concern for people , intent on attaining the godlike powers he had been promised . He also developed a near - obsessive hatred of the Doctor , blindly resenting how the Doctor continually interfered with his plans , incapable of acknowledging the Doctor ' s protests that he would leave Grayle alone if Grayle would abandon his plans for global conquest . ( AUDIO : " Seasons of Fear " )