Which prominent figure opposed the mexican-american war?

Henry Clay Sr.

Explanation:

Henry Clay Sr. was an attorney and politician from Kentucky. The state of Kentucky was represented by him in both the Senate and the House of Representatives of the United States. At the time when the then U. S. President John Tyler made an annexation agreement with Texas clay announced opposition to this annexation. Clay argued that the nation does not require any annexation due to the very fact that it would bring tensions and what the country need is "union, peace, and patience".