Henry David Thoreau was a man who lived a long time ago, in the mid-1800s. He was a writer and philosopher who liked to think a lot about how people should live their lives.
Thoreau spent a lot of time living in a little cabin in the woods by a pond called Walden Pond. He wanted to live a simple life close to nature, and he thought that people should spend more time in the outdoors and less time worrying about things like money and possessions.
Thoreau wrote a famous book all about his time living in the woods called "Walden." In it, he talks about how he tried to live a simple and meaningful life. He was also a big believer in civil disobedience, which means disobeying certain laws that you think are wrong or unjust.
Thoreau was a very wise man who had a lot of important ideas that still matter today. People still read his books and think about what he had to say.