Surt is the King of Fire in Norse mythology, the Lord of the Fire-Giants of the realm of Muspellheim. In the beginning, there was only the blackness of Ginnungagap, and then Surt appeared out of the blackness with his flaming sword and touched land, and it lit up and became the Realm of Fire. Eventually it drew close enough to Niflheim, the primal Realm of Ice, that itwarmed and melted the frozen earth, revealing Ymir the primal frost-giant and Audumhla the Great Cow. In this way, life was created from the meeting of fire and ice in Nordic mythos. Surt's children - the fire-giants - eventually met and intermarried with Ymir's children, and Surt's bloodlines show up in many younger fire-giants such as Farbauti and his son Loki. As such, Surt is the single oldest surviving being in the Nine Worlds. Acording to the primary sources, in the beginning, before there were any other living beings, there was Surt lighting the place up with his great sword - or possibly wand - of fire and light, Laevateinn. Surt himself will not discuss where he came from, or what brought him forth; in fact it's another of the questions that you shouldn't be foolish enough to ask. He does have a temper, and if it rages, you may be in for fire hazards in your life over the next several weeks.
Surt is the godfather of Loki, and raised him as a son in childhood. He has said that he is Loki's godfather, and that Laufey came to Muspellheim to give birth to him, and that she lay in Surt's biggest fireplace to bring him forth. Surt has a close relationship with (and a great respect for) Loki's daughter Hela, with whom he is building the great Ship of Ragnarok, Naglfari, as a joint project; in spite of the fact that he is much older than her, he refers to her as "Her Ladyship", as many etins do.
Surt is knowledgeable in the ways of all kinds of fires, and especially - although few speak to him of this - the kind of primal fire that stars are made of. In fact, his knowledge of suns and stars outside the Nine Worlds is enough to take one aback, and seriously wonder about his origins. It goes without saying that he knows a great deal about moving heat and energy.
According to the Voluspa, if Ragnarok comes to pass, Surt and his children will rise up with the legions of Hela's dead mortals and attack the forces of Asgard. It is prophesied that should this happen, Surt will slay the god Frey, who gave up his sword for love and must defend himself only with a deer antler. Then much of the world will be consumed in flames, and Surt will rebirth it again.