David Peter Gagen (born 11 August 1953) is a former speedway rider from England.
Gagen rode in the top tier of British Speedway from 1972 to 1983, riding for various clubs. He reached the final of the British Speedway Championship in 1977.
In 1977 he competed in the British Speedway Championship final.
In 1982, he earned a testimonial meeting for Boston Barracudas, where he had also become the club captain. He retired after the 1984 season.