Lady Vasarus was a powerful Bronze Dragon who lived in The Peacebond until a few months before the start of the campaign, when she was killed by the Deluvian Deathfin Vazilai. About 16 years before this, she had a relationship with Darius of the Frozen Wastes, which resulted in the birth of a son, who she named Little One.
She was a fierce opponent of slavery (a trait she instilled in her son) which may be why she chose to live away from the other dragons on Haroan and Novendil. This led her to oppose the Deluvian invasion of Verandi, harassing the KT forces with both her immense draconic strength and a lightning breath so powerful that it could slay even the electrically-resistant fish-men. She could therefore be considered to be an unofficial participant in the Laric Counterinvasion.
She may or may not have had some kind of professional or personal relationship with Lord Azhna, as he sent an emissary to extend an invitation to her to meet with him. Then again, his use of death knights clashes pretty heavily with her anti-slavery stance, so it may be that he was reaching out to Dragons at random.
As well as her skill with a sword, she was sufficiently powerful in magic to cast Suggestion on Little One in order to force him to retreat from Deluvian forces without an argument.