There were literally thousands of scientists who participated; if you had to single one out, it would probably be scientific director Robert Oppenheimer.
The Making of the Atomic Bomb has 886 pages.
The ISBN of The Making of the Atomic Bomb is 0-671-44133-7.
Leo Szilard.
In September 1949, the first Russian bomb created a changed situation.
Robert Oppenheimer.
The scientist given the most credit for the building of the atomic bomb is Robert Oppenheimer.
I suggest Richard Rhodes book The Making of the Atomic Bomb.
Leo Szilard invented the atomic bomb in 1933, but no one person can be credited with creating it. Remember the US spent $2,000,000,000 on constructing and operating the huge industrial infrastructure needed to build them before a single bomb could be built!
The atomic bomb was developed during World War II as part of the Manhattan Project. The project was spearheaded by the United States and led by scientists such as J. Robert Oppenheimer, who is often credited as the "father of the atomic bomb."
No single person can be credited with developing the atomic bomb. Robert Oppenheimer and Albert Einstein were among the well-known people.
I suggest reading Richard Rhodes book: The Making of the Atomic Bomb.
No German scientist discovered the Atomic Bomb, so this question is meaningless. A Hungarian scientist, Leo Szilard, invented the Atomic Bomb in 1933 and he was already in London when he did it. It took 12 more years for the US to eventually make the first ones.