Irving Kahn was one of Graham's teaching assistants at Columbia University in the 1930s. He was a close friend and confidant of Graham's for decades and made research contributions to Graham's texts "Security Analysis", "Storage and Stability", "World Commodities and World Currencies" and "The Intelligent Investor". Kahn was a partner at various finance firms until 1978 when he and his sons, Thomas Graham Kahn and Alan Kahn, started the value investing firm, Kahn Brothers & Company. Irving Kahn remained chairman of the firm until his death at age 109.