The mighty two-handed sword Ice, ancestral sword of the House Stark, was forged from Valyrian steel. In the very first episode of the fantasy epic, Eddard ("Ned") Stark, Lord of Winterfell, used this heirloom to behead a deserter of the Night's Watch. Later in the first season (Baelor, Episode 9), this very same sword was the one used for Eddard's own execution on the steps of the Great Sept of Baelor in King's Landing.
At the very beginning of the first episode of the fourth season, Tywin Lannister had it melted down and re-forged into two new swords, Oathkeeper and Widow's Wail.