Blenheim is a giant commander of the Whitebeard Pirates. He is roughly the size of Whitebeard. It is unknown which division he leads.
He is a large man with a dark ponytail hairstyle and a light beard. He wears a vest and the silhouette Whitebeard Jolly Roger can be seen tattooed on both of his biceps. He carried a sword at one point.

(Source: One Piece Wiki)