Rostnstal

[Atoli]

I refuse to learn from that guy! xD
I'm from 1.0 Limsa, so despite only realizing 3 days ago that half of the past main scenario I saw was only the Echo showing me Rostnsthal's memories, I do remember that he was a bad guy ten years prior to the 1.0 storyline :O

More useful answer:
He once was known by the name Sthalmann and was the right-hand man of the Admiral back when they were still just the strongest pirates, unlike nowadays.
But his lust for power took over and he kind of sacrificed his crew to have them fight an unneccessary skirmish with the Sahagin so he could (probably murder the Admiral, although it's just known that he was killed at a convenient time) get his hands on an artifact of unlimited power. In the end he loses both the artifact AND his crew and and 10 years later, when he first encounters the player, he is merely a pitiful drunkard who has trouble paying his debts and brooding over the loss of his crew. He kind of helps the player a few times, but still...xD