"Lord Andaren was young, but he was definitely not a fool. After his failed attempt to block King Aegon from passing through the Borderlands, many of his men expected that he would ride towards Storm's End to save his king. But Andaren...did nothing. And because that, we avoided the risk of going extinct. "
Trevyr Blackgard[src]
Andaren Blackgard, also known as Andaren the Oathbreaker, is an unseen character Game of Thrones. He is deceased when the series begins and has only appeared in the Histories & Lore featurette, House Blackgard (Histories & Lore).

Andaren was the Lord of Ebonheart during the War of Conquest. After Aegon the Conqueror passed through the Borderlands, unscathed, Andaren was expected to save King Argilac Durrandon from Orys Baratheon's forces. Instead, he turned his back on Argilac and stayed in the Borderlands, avoiding going to war with the Targaryens.