A superstar usually is someone who has become famous in sports, or films, or popular music, someone like the famous singer Michael Jackson. One of the most famous sports superstars in the United States was the boxer, Muhammad Ali. As a young man, he won a gold medal in the Olympics as a boxer. Then he become the heavy weight boxing champion of the world. Before long, he was known as one of the greatest boxers in sports history. Once Ali said when he was a champion he was more famous than the president of United States or the head of any other country in the world. The word 'super' means something that is good, and of course, a star is a person who is famous. So people use 'superstar' to describe the top people in sports, films or music. But like the stars in the sky, a superstar disappears as time goes by. Many people, for example, know little these days about Ali or Jackson. Superstars are you loved by millions of people today, but often forgotten tomorrow. Michael Jackson is famous for his ______ but Muhammad Ali for his ______.