Theodore Roosevelt was the 26th president of the United States, taking office at the young age of 42 after President McKinley's assassination. He is known for his progressive reforms and assertive foreign policy, including constructing the Panama Canal and establishing the Roosevelt Corollary to the Monroe Doctrine. Roosevelt had a privileged early life but struggled with asthma. He later served as a lieutenant colonel and war hero in the Spanish-American War before becoming governor of New York and then president in 1901.