Chief Seattle, also known as Sealth, Seathl or See-ath (around 1786-1866) was an American Indian leader of Suquamish and Duwamish Native American tribes, settled in the territories that now belong to the state of Washington. Facing a historic moment and a hostile environment, the Indian chief rose as a peacemaker with the English colonists, converting to Catholicism and seeking a secure accommodation for the white man. He maintained a close relationship with David Swinson Maynard, one of the founding fathers of Seattle and also an active fighter for the rights of native Amerindians. It was Maynard in fact who gave him the rank of Chief.
Seattle is now considered one of the greatest leaders of the environmental movement thanks to the letter that he sent in 1855 to Franklin Pierce, President of the United States, which, among other things, highlighted the importance of taking care of resources natural, summarizing his thought with this phrase: "Whatever befalls the Earth, befalls the sons of the Earth."
You can read the complete letter from Chief Seattle to Franklin Price here.