Abraham Klaassen was a merchant ship owner in Amsterdam who traded between Holland and North Sea ports. His ship carried a miscellaneous cargo (Dutch merchandise and products) to other North Sea ports and brought back to Holand merchandise (farm implements, etc.) picked up at these trading posts.
He was a Mennonite. He married Catarina Dicken (1724-1779) and they had eleven children, eight of whom died very young. Three boys grew to manhood, including Johan.