Iyannough was a chief and a sachem for the Mattakese tribe. They were a subgroup of the Wampanoag people. The plaque states that Iyannough was a Wampanoag chieftain. Interesting omission. 

A story that directly links Iyannough to the Pilgrims of the Mayflower is that he assisted in finding the son of John Billington—a passenger aboard the vessel. Supposedly leading to solid relations between the Pilgrims and native peoples. Until the death of Iyannough. Wherein then understanding “deteriorated.” The peace may have also been good due to the amount of land Iyannough gave the settlers. Like where Martha’s Vineyard is today.