You should say:

　　- who this person is

　　- (how he or she became a leader)

　　- what this person did (has done) that you admire

　　- how you know this person or know about this person

　　and explain how ( = why) this leader's qualities impressed you.

　　范文

　　Times need heroes, and heroes stand out. Franklin Roosevelt is just a hero of the times. Well known for his unprecedented 13 years as the President of U. S. , he is regarded as a savior of America. However, it is not his brilliant achievements that attract me. What I really admire are some qualities shining in his whole life such as fortitude, courage and also his amiability.

　　His early time, I mean before his forties, was smooth. He was born rich and had a happy marriage. After graduating from Harvard, he served in the Navy. At that time, he had already shown his remarkable leadership and since his uncle was a President, he would surely enter the political arena. But everything changed when he was 39. Healthy and strong as he was, he was attacked by polio after swimming, which caused the life long deformity in his legs. It was extremely hard for this ambitious man to face the misfortune. He was, of course, in a bad mood and wanted to give up all his dreams at first. Then, after careful thinking, he finally decided to bestir himself. He was not a man easy to surrender. Again he took part in political activities and, at the same time, practiced standing up and then walking with a stick. Eventually this brave man won the battle against fate. He became the only disabled President in American history and unprecedentedly served four terms. All should be attributed to his fortitude.

　　"The only thing we fear is fear itself." This famous saying now has spread all over the world and encouraged lots of people. Roosevelt first said it, and as a great leader, he made all his people believe it. He practiced what he preached for he was surely a courageous person challenging the tradition. He formulated new policies to help his nation out of the Depression. He declared war against Fascists though most of the Congressmen opposed him at that time. All proved that he was right for his courage was not rash but based on careful thinking. "A leader is one who dares to dream, and then, dares to achieve."

　　He was great, but not great in appearance. He looked like a kind grandpa at the first sight. He initiated the fireside chat to express his ideas and explain his policies in a relaxed atmosphere on radio. He always smiled sincerely when speaking and listening. These didn't lower his prestige but made him amiable and welcome.

　　He is surely not a perfect man no one can be perfect. Every age has its hero in the forefront, just like Franklin Roosevelt, a man I admire.