Franklin D. Roosevelt was the President of the United States, which means he was the boss of the whole country. He was the boss for a really long time, from 1933 when he first became President, until 1945 when he died.
After being President for two times, which is usually the maximum time anyone can be the boss, he decided he wanted to be the boss again. So, he ran for President again, and won! This was called his third term as President.
He was the boss for a really long time, and during that time, he did lots of important things like helping people who didn't have jobs find work, and helping the country prepare for a big war that was happening in Europe.
Then, after a few years, he decided he wanted to be the boss again! So, he ran for President one more time, and won! This was called his fourth term as President.
Sadly, during his fourth term, he became very sick and died before he could finish being the boss. No one else has ever been the boss for as long as Franklin D. Roosevelt, and he is remembered as one of the most important and influential Presidents the United States has ever had.