Ryan used to be a warrior, he was a Guard to protect Mulgore and the Thunder Bluff. When the Centaurs invaded Mulgore, Ryan took up arms and fighted against the Centaurs.
One day, Ryan has been surrounded by a team of Centaurs, he fighted and killed them all. But his right arm was seriously injured. There was no way to cure the arm when he came back to the camp. The horde doctor had to cut Ryan's right arm off.
Blood Hoof, the chief of Thunder Bluff, was sad to heard about it. He invited the most famous Goblin engineers from Orgrimmar to help Ryan. They made a prosthetic arm with a cannon attached to it and equiped it on Ryan.
From then on, Ryan has a new lease of life, and was appointed general of the siege legion of Tauren.