Shantideva was a very wise and kind teacher who lived a long time ago in a country called India. He taught people about how to be happy and kind to others.
One thing that Shantideva taught was about a special type of thinking called compassion. Compassion means that you feel sorry for someone who is having a hard time or is suffering. And when you feel compassion, you want to help them feel better.
Shantideva also taught about something called bodhicitta. This is a big word that means "awakening mind" or "wish to become enlightened." It's like having a very big dream to help yourself and others become the best they can be.
Shantideva wrote a book called "The Bodhisattva's Way of Life" which talks about how to be a really good and kind person. Many people still read and learn from this book today.
In short, Shantideva was a wise teacher who taught people about compassion and a big dream to help others become better. He wrote a book about it which is still read by many people today.