Benjamin Graham was an influential American economist and investor who is considered the father of value investing. He wrote two influential books, Security Analysis and The Intelligent Investor. The Intelligent Investor teaches the distinction between investing and speculation, with investing focused on analyzing companies and protecting against losses, while speculation aims for extraordinary gains. It also covers topics like how to select stocks, dealing with market fluctuations, and the importance of a margin of safety. The book has been hugely influential on investors like Warren Buffett and remains one of the foundational texts on value investing.