Former Lt. colonel in the Rough Rider Regiment during the Spanish-American War

Answer: Theodore Roosevelt Jr. Explanation: The Rough Riders was a nickname given to the 1st United States Volunteer Cavalry, one of three such regiments raised in 1898 for the Spanish-American War and the only one to see combat. The United States Army was small, understaffed, and disorganized in comparison to its status during the American Civil War roughly thirty years prior. Following the sinking of the USS Maine, President William McKinley needed to muster a strong ground force swiftly, which he did by calling for 125,000 volunteers to assist in the war. The U. S. had gone to war in opposition to Spanish colonial policies in Cuba, which was then torn by a rebellion. The regiment was also nicknamed "Wood's Weary Walkers" for its first commander, Colonel Leonard Wood. This reflected their dissatisfaction that despite being cavalry, they ended up fighting in Cuba as infantry, since their horses were not sent there with them.

Wood's second in command was former Assistant Secretary of the Navy Theodore Roosevelt, a strong advocate of supporting of the Cuban War of Independence. When Wood was promoted to become commander of the 2nd Cavalry Brigade, the regiment became known as "Roosevelt's Rough Riders." That term was borrowed from Buffalo Bill, who called his travelling Western show "Buffalo Bill's Wild West and Congress of Rough Riders of the World".