Rex McDonald was an American Saddlebred stallion. He was only beaten three times in his show career and had an influential career as a sire.

Rex McDonald was foaled on May 30, 1890, in Callaway County, Missouri.^[1][2] He was sired by Rex Denmark and out of Lucy Mack. He was a black stallion standing 16 hands (64 inches, 163 cm) high and was bred by Joe McDonald.^[1] After breeding Rex McDonald, Joe McDonald became ill and began selling his horses. Rex McDonald was sold to R. T. Freeman as a yearling for $105, alongside his dam. In 1894 he was sold to John Hughes of Kentucky for $3,050. He was sold several more times and at one point during his breeding career was owned by a group of businessmen.^[1] Rex McDonald died November 13, 1913, and was buried in the fairgrounds at Mexico, Missouri,^[3] although the body was later moved to Tom Bass's property and still later reburied at the American Saddlebred Museum in Mexico, where it remains.^[4][5]

Rex McDonald was a five-gaited horse who was initially trained by Billy Davis.^[3] Later on he was trained and shown by Tom Bass, a notable horse trainer born a slave, who trained horses for Theodore Roosevelt and Bill Cody.^[6] In 1893 Rex McDonald was shown for the first time at the St. Louis National Horse Show and won a championship.^[7] At the time, there was a strong rivalry between Kentucky and Missouri about which state produced the best Saddlebreds, and Rex McDonald was a star for the Missourians. Ironically, he was later sold to a Kentucky owner.^[3] He was only beaten three times in his career.^[2] At one show, he beat his own sire, Rex Denmark. He was finally retired to stud because few people were willing to show against him.^[1]

Rex McDonald sired over 200 colts that were registered with the American Saddlebred Horse Association.^[1] One of his colts was a pacer and was harness raced.^[8]