During the 1930s, the Huntington Herald-Dispatch started running drawings of an unidentified human-like buffalo in its sports section. By 1954, Marshall College had named the buffalo "Marco." He was the brainchild of Jack and Vause Carlsen who were the editors of Marshall's yearbook, The Chief Justice, that year.

The actual Marco mascot, a student dressed up in a buffalo costume that is often seen at Marshall events, first showed up in 1965. Also that year the students, faculty, and administration voted to change Marshall's nickname from the "Big Green" to the "Thundering Herd." Marshall had used both nicknames for decades. The first mention of the "Thundering Herd" nickname came from former Herald-Dispatch sports editor Duke Ridgley, when he referred to the Marshall football team as the Thundering Herd after it defeated Glenville State Teachers College, 26-0, in the opening game of the 1925 season. That was the same year that The Thundering Herd, based on a novel by Zane Grey, was showing in the movie theaters.

Marco the buffalo has embodied the Herd for generations of Marshall fans. The mascot's outfit has changed several times throughout the years. His current look was introduced in the fall of 1985, and six years later Marshall student Allen Young won the national championship of college mascots.