What cavalry regiment — known as the “Rough Riders” — did Teddy Roosevelt join during the Spanish-American War?

What cavalry regiment — known as the “Rough Riders” — did Teddy Roosevelt join during the Spanish-American War? 1st U.S. Volunteer Cavalry Regiment 2nd U.S. Volunteer Cavalry Regiment 3rd U.S. Volunteer Cavalry Regiment 4th U.S. Volunteer Cavalry Regiment 5th U.S. Volunteer Cavalry Regiment The correct answer to this quiz is 1st U.S. Volunteer Cavalry Regiment.