Dain (translated Dine in some of the fan translation) is one of the Twelve Crusaders, possesses the title of Dragon Knight, is the original wielder of the Gungnir, and is the founder of Thracia.
Dain's known blood descendents are: Travant and Areone. His sister is Noba.
According to some sources, Dain and Noba's lives took a turn for the tragic in what's known as the "Tragedy of the Gáe Bolg". Among the Thracian Knights there was an old friend of Dain; he and Noba fell in love, and they got married with Dain's blessing. However, some time after the war, Dain and his brother-in-law fought for reasons undisclosed, and eventually started dueling each other...
Noba tried to stop the fight, but she accidentally killed her spouse with the Gáe Bolg. She committed suicide to join her husband in death, and few years later Dain also died in mysterious circumstances. Ever since then, Manster and Thracia have had huge difficulties.
Etymology
Dain is the name of three separate figures from Norse mythology.
Trivia
Dain is the only crusader with no playable descendants. However, in the Final Chapter, Altena can talk to Areone, causing him to become an allied NPC.