Tedosian is a High Lord of Tear and married to Alteima. Shortly after accidentally killing his friend Carleon in a hunting accident, he fell ill when his wife poisoned him. The whole thing was orchestrated by Thom Merrilin who had discovered that Tedosian was plotting against Rand. Tedosian is still alive and plotting, but effectively incapacitated by Thom's devices.
For more details on Tedosian, visit Encyclopaedia WoT.