Giacomo (foaled February 16, 2002 at Mill Ridge Farm near Lexington, Kentucky) is a Thoroughbred stallion race horse trained by John Shirreffs, who is perhaps best known for winning the 2005 Kentucky Derby in 2:02.75. At odds of 50–1, Giacomo stands as tied, with Mine That Bird in 2009, for the second-biggest longshot ever to win the Derby, trailing only Donerail, who went off at 91–1 in 1913. Giacomo's owner received a first-place check of $1,639,600 for the victory, the largest in Kentucky Derby history. Mike E. Smith was Giacomo's jockey when he won the Derby. Smith had also ridden Giacomo's sire, 1994 Eclipse Award for Horse of the Year winner Holy Bull, in that year's Derby, when the 2–1 favorite was bumped coming out of the gate and finished 12th. Giacomo finished third in the 2005 Preakness Stakes behind the favorite, Afleet Alex. He finished seventh in the 2005 Belmont Stakes, again behind the favored Afleet Alex; Smith said after the race that the horse had breathing problems.
Giacomo continued to race after his disappointing Belmont finish. In his first race back, he finished third in the Strub Stakes at Santa Anita Park. After that, he was raced in the prestigious Grade I Santa Anita Handicap, where he finished 5th and was never a threat. After a four month layoff, Giacomo won the July 22, 2006, San Diego Handicap by a head. The victory was followed by a 5th in the Pacific Classic Stakes and a show in the Goodwood Breeders' Cup Handicap, where Giacomo lost to Lava Man for the 3rd time in 4 races. Despite the fact that Giacomo had only won two stakes races, he was entered in the 2006 Breeders' Cup Classic field, where he faced Lava Man as well as other top horses such as Bernardini and the eventual winner, Invasor. Giacomo finished fourth.
After the race, it was announced that Giacomo would be retired to stud at Adena Springs in Kentucky.
The gray stallion is owned by his breeder, Jerry Moss, who may be better known for co-founding A&M Records with trumpeter Herb Alpert. Giacomo was named after the son of Sting, who recorded for A&M both solo and with The Police, rather than for the Italian composer Puccini. Giacomo's half-brother, Tiago, is also a race horse. Giacomo and Tiago both mean James, the first being Italian and the second, Portuguese.