I assume that you are asking who was the president of the United States in 1942. If that is what you are asking, the answer is that the president in that year was Franklin Delano Roosevelt. He is often known by his initials -- FDR.
Roosevelt was distantly related to Theodore Roosevelt, who was president early in the 1900s. Do not confuse the two of them.
Franklin Roosevelt is one of the most important presidents in US history because he was president during both the Great Depression and most of World War II.
He is the only president ever to be elected more than twice. He was elected 4 times but died a little way into his 4th term. Since then, the Constitution has been amended so no one can be president for that long.
In 1942, the President of the United States was Franklin Delano Roosevelt.