Who was theodore roosevelt and how was he affected by succession?

Theodore Roosevelt was born on October 27, 1858 into a prosperous Dutch New York City family, he was a sickly, asthmatic child, then he was an athlete and books writer, the best known which is "The Winning of the West", was a great hunter and animal collector, always had a nickname "Teddy", by which everyone called him, He had several public offices, until becoming the vice president of William McKinley, later that year he would become the twenty-sixth President of the United States and the youngest President yet at 43 years old, a sudden succession, which, of course, nobody expected, since the Republicans of that time had nominated him to the vice presidency thinking that it would be an unimportant position.