Who was a proponent of the policy of assimilation in the early 1800s

President Jefferson.

Explanation:

During the early 1800s, a policy was adopted in the United States Federal Laws named assimilation policy. The policy was proposed by Thomas Jefferson, the third President of the United States. The proponents of this policy viewed it as a means of survival of Native Americans in the changing white-dominated society.

Though this policy required acculturation or assimilation of American-Indians into European-American Society. According to this policy, Native American Indians, who accepted the individual allotment were granted as a U. S. citizen. Among many Native groups, Hoofs was the one who accepted Jefferson's assimilation policy.

So, the correct answer is President Jefferson