Grey (Called Slate in the American version) was once an Arachnian knight who was a good friend and rival to Igneous. They were both known as the legendary "Fang and Claw" to everyone. However, he left the rank of knights a long time ago but came back and challenged Igneous to a duel to the end. Hunter did a little investigating and found out Grasshop took a pendant of value from Grey and said he would return it once Grey defeated Igneous. In exchange for defeating Igneous, Grasshop agreed not to destroy Grey's village. Hunter and Shadow were able to successfully drive away Grasshop's occupation force. Even though the Invectids were gone, the two knights still fought and they concluded that they were equally matched. A few episodes later, Grey had arrived to help Arachna against an Invectid invasion, but it had been already driven off. However, Prince Lumen left him in charge of Arachna castle while the Spider Riders helped the people of Nuuma.

Source: Wikipedia