When did Plenty Coups become the head chief of the Crow Indian people?

When Plenty Coups was about 55 years old, he became the head chief of the three bands of the Absaaloga. Each of the three bands, called the River Crow, the Mountain Crow and the Kicked In The Bellies, also had a sub-chief. The three bands lived in different areas, but they needed one chief to speak for all of them. Plenty Coups became the head chief of the Crow Indian people in 1903 after Pretty Eagle died. Pretty Eagle was the major chief until that time. Plenty Coups was accepted as the head chief of the three Crow bands. The River Crow, the Mountain Crow of which Plenty Coups was chief and a third group, centered in Wyoming and called the Kicked In The Bellies, each had their own chiefs. During this era bands were negotiating with the United States government and different military groups. It was necessary to have one person who was looked upon as the head chief of all of the groups. It took a unique person to be accepted by all three groups, and Plenty Coups was one of those rare individuals. From: Chief Plenty Coups State Park Museum Tour Content

Just as in any political system, there are different kinds of parties, but it's not so much River Crow or Mountain Crow anymore. These parties evolved because they migrated along certain paths; they left certain bands due to deaths or births; or they mingled with different tribes. This is how the three largest bands originated. The River Crow died out in the 1600s, and the few that remained migrated to Mountain Crow which was this area. The original River Crow lived south of the Dakotas when the splitting of the tribe occurred. They stayed along the Missouri, and we now know had a village near Glendive, Montana. They lived in adobe huts. When they migrated, they found it easier to use teepees.
The Kick In The Bellies were the ones that adapted to white man's society and religions. They based themselves along the river to trade goods and sell lumber to the steamships. They were considered the most neutral of the tribes because they modernized while everyone else kept their traditional ways. Once the reservation was established, all Crow Indians had to settle as one. That is where they all became Mountain Crows. Even though, you will sometimes still today hear people referring to themselves teasingly as either River Crow or Mountain Crow. From: Vincent Goes Ahead, Jr., Museum Interpreter, Vice Chairman of the Crow Tribe