The Arapaho are an indigenous people historically living on the plains of Colorado and Wyoming. They were close allies of the Cheyenne tribe and loosely aligned with the Lakota and Dakota.

By the 1850s, Arapaho bands formed two tribes, namely the Northern Arapaho and Southern Arapaho. Since 1878, the Northern Arapaho have lived with the Eastern Shoshone on the Wind River Reservation in Wyoming and are federally recognized as the Arapahoe Tribe of the Wind River Reservation. The Southern Arapaho live with the Southern Cheyenne in Oklahoma. Together, their members are enrolled as the federally recognized Cheyenne and Arapaho Tribes.

The Arapaho language is currently spoken in two different dialects, and it is considered to be a member of the Algonquian language family.

Resource:  https://en.wikipedia.org/wiki/Arapaho#Powder_River_Expedition