Harry Sullivan Surgeon Lieutenant Harry Sullivan was a Royal Navy surgeon in the employ of UNIT and a companion of the Fourth Doctor . He later worked for NATO and MI5 . He had a younger step - brother named Will . ( AUDIO : " Buried Secrets " ) Biography . Career with UNIT . Harry first encountered UNIT while he worked in the Royal Navy , at the same time the Third Doctor had briefly left Earth in his TARDIS for Peladon . ( PROSE : " The Face of the Enemy " ) After he had joined UNIT and the Third Doctor was apparently in a coma , the Brigadier summoned " Dr Sullivan " to help see him through the process . When Sergeant Benton woke the Doctor by offering him a cup of coffee , the Brigadier cancelled the call for Dr Sullivan ' s assistance . ( TV : " Planet of the Spiders " ) Three weeks after confronting the Great One on the planet Metebelis III , the Doctor and his TARDIS re - appeared in his laboratory at UNIT HQ . The Doctor had received a fatal dose of radiation , forcing him to regenerate or die . ( TV : " Planet of the Spiders " ) Harry Sullivan arrived on the scene just moments after the Doctor regenerated into a new form . ( TV : " Robot " ) Adventures with the Doctor . After the defeat of the robot K1 , Harry found himself in the Doctor ' s TARDIS . ( TV : " Robot " ) At first very much confused , he trailed the Doctor and Sarah Jane Smith to Space Station Nerva , where they were pitted against the Wirrn . ( TV : " The Ark in Space " ) They then travelled by transmat from the space station to an uninhabited far future Earth . Harry fell into a trap set by the stranded GalSec colonist Roth , but was able to find a way out . He later tried to help a dying dehydrated prisoner held captive by Styre for his experiments , but was too late . He looked after Sarah when Styre ' s experiment caused her to pass out from fear . Under the Doctor ' s instructions , Harry removed the terullian diode bypass transformer from Styre ' s ship , which caused the energy Styre fed on in his ship to feed on Styre instead . ( TV : " The Sontaran Experiment " ) Heading back to the beacon , the Time Lord s intercepted the transmat beam and took them to Skaro to prevent the creation of the Daleks . ( TV : " Genesis of the Daleks " ) Via time ring , they travelled back to Nerva , but to a much earlier year . There he helped save Voga from the terror of the Cybermen . They then received a summons from the Brigadier on the space - time telegraph calling them back to 20th century Earth . ( TV : " Revenge of the Cybermen " ) Immediately after his adventure with the Cybermen , Harry was ejected from the TARDIS and it stranded him in England , 1936 . There Harry met the Eighth Doctor , who had no memory of Harry or any of his previous adventures . Harry helped the Eighth Doctor to stop a Dryad from turning the land of Britain on the people that lived upon it . The Fourth Doctor and Sarah picked Harry up shortly after . ( PROSE : " Wolfsbane " ) Back in the late 20th century , Harry rejoined UNIT to defeat the shape - changing Zygon s and their giant , dinosaur - like beast , the Skarasen , in Scotland . After the Zygons ' defeat , Harry decided to return home to London by train rather than by TARDIS . ( TV : " Terror of the Zygons " ) Sometime after the attempted Zygon invasion , Harry developed a Zygon - killing gas called Z - 67 while working on captive Zygons at Porton Down . However , the gas was confiscated by the Doctor . ( TV : " The Zygon Invasion " / " The Zygon Inversion " ) When the Doctor and Sarah returned to Earth , Harry helped them against the Kraal s , who had also created an android duplicate of him . ( TV : " The Android Invasion " ) At some point during his UNIT career , Harry was put in charge of a team and sent to the West Country to investigate a missing UNIT team member and a subsequent series of " monster " sightings . He met up with the Ninth Doctor and his companions , Rose Tyler and Jack Harkness , and together they found the missing man and solved the mystery of the " monsters " . ( COMIC : " Official Secrets " ) Post - UNIT career . In the early 1980s , Harry worked at NATO . ( TV : " Mawdryn Undead " , PROSE : " Harry Sullivan ' s War " ) By 1997 , he was Deputy Director at MI5 . At that time , via the agency of time travel , he met up once again with a familiar version of the Doctor , as well as a much younger Sarah Jane Smith , for whom little time had passed . ( PROSE : " System Shock " ) He still worked for MI5 in 1999 , ( PROSE : " Millennium Shock " ) and became Chief of Staff at some point prior to 2015 . ( PROSE : " Damaged Goods " ) By 2005 , he was back at NATO , having achieved the rank of Commodore . The Brigadier asked him for a favour at the time . ( AUDIO : " The Wasting " ) To commemorate an anniversary date , Sarah Jane had yearly meetings with Harry Sullivan . By 2006 , Harry had been missing in action for some time , though Sarah kept coming to the same place they used to meet . She " talked " to him and raised a toast to him wherever he was . ( AUDIO : " Buried Secrets " ) Harry was still missing in 2009 . ( PROSE : " The Wedding of Sarah Jane Smith " ) In 2010 , Sarah Jane recalled that Harry had worked in developing vaccines that had saved thousands of lives . ( TV : " Death of the Doctor " ) In June 2015 , though , Harry was alive and discovered a possible cure for HIV in blood taken from David Daniels . ( PROSE : " Damaged Goods " ) Alternative timelines . A parallel Earth version of Harry served on a nuclear submarine in a world taken over by the Silurian s after the death of the Third Doctor . He saved the life of the Seventh Doctor ' s companion Bernice Summerfield . ( PROSE : " Blood Heat " ) Undated events . At some point , a photo of Harry existed in UNIT ' s Black Archive alongside Sergeant Benton and Sarah Jane to record him as a companion of the Doctor . ( TV : " The Day of the Doctor " ) In the Hellscape . A version of Harry appeared in a " hellscape " dream the Eleventh Doctor created while the mind parasite Mr Waites fed off the worst thing Doctor could imagine . In the dream , the Doctor worked with Harry at the Department of Commonality . Harry revealed that the protest at the " square " was much larger than reported and that his sister ' s boyfriend had proof on his camera . After the Doctor didn ' t enjoy working at mediation and wanted to return to records , he reported to Mr Waites about the camera , and the peace officer s arrested Harry . ( COMIC : " John Smith and the Common Men " ) Personality . Harry was rather old - fashioned and stereotypically English in his attitudes . He often employed slightly archaic language , referring to Sarah affectionately as " old girl " or " old thing " — which somewhat annoyed her . ( TV : " The Sontaran Experiment " , PROSE : " Doctor Who and the Ark in Space " ) He was brave , one time saving the Fourth Doctor ' s life from a landmine on Skaro . ( TV : " Genesis of the Daleks " ) He had a " can - do " attitude , adapting well to the many strange situations in which he found himself . He could , however , be quite clumsy and unsubtle . This led the Doctor to declare in a moment of frustration , at the top of his lungs that " Harry Sullivan is an imbecile ! " , before passing out from the effects of a rockfall on Voga – caused by Harry . ( TV : " Revenge of the Cybermen " ) He flirted a bit with Sarah . Despite an outward annoyance at that attitude , once when thinking him dead , Sarah admitted she found it endearing . ( PROSE : " Wolfsbane " ) He was good at cricket , and was able to throw a cricket ball over at least a metre . ( PROSE : " Doctor Who and the Ark in Space " ) Relatives . Harry had a step - brother named Will , whom Sarah Jane Smith met in 2006 . ( AUDIO : " Buried Secrets " ) Will was killed by Josh Townsend shortly after meeting her . ( AUDIO : " Fatal Consequences " )