Complex sentence: The first published letter in the August 1959 issue of "Action Comics" was written by an eleven-year-old from Garland, Texas named Dave Mitchell, who would go on to become a well-known Miami radio personality.
Split into simpler sentences: The first published letter-of-comment in the August 1959 issue of Action Comics was from an eleven-year-old reader from Garland, Texas named David Mitchell. The same Dave Mitchell would go on to become a well-known Miami radio personality.