Thatch

Thatch was the commander of the 4th Division of the Whitebeard Pirates, until he was killed by Marshall D. Teach.

Appearance
‎Thatch had blonde hair, which went to a point at the back of his head, and some black stubble around his chin. Thatch also had a scar running down his face and had his teeth usually clenched. Thatch also dressed poshly, usually in blue uniform.

Abilities and Power
Having been a division commander, he had authority over a vast number of subordinates. Given this, Thatch may have had prowess equal to that of the other division commanders if not higher. Also, if it were not for the murderous intervention of Marshall D. Teach, Thatch would have eaten the Yami Yami no Mi; a uniquely powerful Logia-type Devil Fruit.

From the anime screen shot, Thatch is seen with a sword on his waist. He might be a swordsman.

The New Comrade
Thatch was one of the first to try befriending Ace when he had arrived on the ship. Ace responded cynically, and questioned that why he is not held with shackles while on board of the Moby Dick, Thatch merely gave an amused look, as though he believes that was unnecessary.

Getting the Yami Yami no Mi and fight with Blackbeard
Thatch later found the Yami Yami no Mi, the Devil Fruit that Blackbeard was after for a long time. This Devil Fruit was the very reason that Blackbeard joined the Whitebeard Pirates, so he killed Thatch and ran off with it, leaving his former commander, Portgas D. Ace, to hunt him down for revenge.

Trivia

 * Seeing a resemblance between Thatch's name and that of the alias of the real life Blackbeard, Edward Thatch, a fan asked Oda, in a SBS question, if Thatch was based on the real life Blackbeard along with Edward Newgate and Marshall D. Teach. Oda replied to the fan that he indeed based Thatch's name on the real life Blackbeard's alias. However, the basis is in name only.
 * During the war at Marineford Whitebeard is seen with only 14 division commanders, minus Ace, instead of 15, hinting that Thatch has yet to be replaced.