Phinis Gestor resides in The College of Winterhold and provides Conjuration spells and Expert level training. Though it is Gestor who remarks that Necromancy is no longer the taboo subject of study it once with the Mage's Guild which was prominent in Cyrodiil during Tamriel's Third Era, he admits that there are few places where "his line of work" can be practiced "without fear of persecution".
 Personal Quest
Once the Dragonborn succeeds in building his/her Conjuration skill level to at least 90, Gestor will grant the Dragonborn a spell to summon an Unbound Dremora Lord on the rooftop of the Hall of Attainment at the College. The purpose of the ritual is to coerce the summoned Dremora to aquire a Sigil Stone from the realm of Oblivion, though naturally this will involve a trial of strength where the Dragonborn must defeat (and resummon) the Dremora Lord twice in combat before it will agree.
The Dragonborn is rewarded with the Sigil Stone upon summoning the Dremora Lord a third time, which s/he can then deliver to Gestor who grants him/her a free Summon Flame Thrall spell. Additionally, the Dragonborn may purchase more spells to summon additional elemental/dead Thralls from that point on. These are costly Master level spells (in both Magicka and Gold!) that will summon Atronachs or reanimate powerful bodies without limit in duration (they can still be defeated by opponents in combat).