This is the cinematic trailer of World of Warcraft: Wrath of the Lich King. The dragon's name is Sindragosa, the Frost Queen. Watch the trailer as Arthas Menethil, the Lich King summons a great Frost Wyrm to do his bidding.
King Terenas to Arthas: "And I know you will show restraint when exercising your great power."
The cinematic trailer is shown after finishing the "Where Dragons Fell" quest in Wrath of the Lich King. Here's an in-game screenshot of Sindragosa's Fall, the location of the trailer.
Not much of a restraint here in exercising power. He's actually a show-off. xD Anyway, Sindragosa looks so awesome and cool (and cold) in this video. Just look at how Frost Wyrms look like in Warcraft III.
Download the WotLK cinematic trailer