Frank Koestner (b. 1953) worked at Cantor Fitzgerald in the World Trade Center. He was killed in the terrorist attacks of September 11, 2001.

Koestner was a stock trader for Cantor Fitzgerald, who loved jogging, skiing, hiking, biking, and whitewater rafting. He was the loving father to a 5-year-old daughter, and he also left behind a fiancé he was planning to marry on Oct. 28, 2001. "He was articulate and educated and ethical," said Dominick Schook, his friend for 31 years.