Hehyal is the clan chief of the Taardad Aiel and was of the Dawn Runner Aiel warrior society before becoming clan chief. He was seen by Aviendha through her visions in her second visit to the glass columns.
Hehyal killed many Seanchan. He was slated to go to Rhuidean and go through the glass columns and become clan chief, but was unable to because of the Seanchan siege on Rhuidean. He still becomes clan chief, but is unable to complete the ritual.
He and Oncala carried out a successful plan to get the rulers of the Westlands to aid the Aiel in their war with the Seanchan. They gave Talana, either daughter or grandaughter of Elayne Trakand, Seanchan plans. These were plans to assassinate Talana and attack the various nations of the Westlands: Caemlyn, Illian, Tear, and the Two Rivers. However, they held back the information that the plans were only contingency plans to be carried out only if the nations of the Westlands went to war with them. This causes the nations to go to war with the Seanchan which leads to the events that will eventually cause their downfall.