Hello there! Let me explain who Sergei Rubinstein is in a way that is easy for a 5-year-old to understand.
Sergei Rubinstein is a person, just like you and me. He was born in Russia, a big country far away from where you are right now. He is famous for being a scientist, which means he studies things in the world around us to learn new things and make discoveries.
One of the things that Sergei is really good at is studying the human brain. You know that your brain is what makes you think, feel, and do things, right? Well, Sergei Rubinstein studies how the brain works, why it does what it does, and how we can better understand it.
He has written a lot of books and papers about the brain and how it works. People all over the world read his work and learn from it. He has even won awards and been recognized by other scientists for his great contributions to our knowledge of the brain.
So, in short, Sergei Rubinstein is a very smart person who studies the brain to help us learn more about how it works. Just like how you learn things in school, Sergei is always learning new things too!