Kauto Star (19 March 2000 – 29 June 2015) was a French-bred National Hunt champion thoroughbred racehorse trained by Paul Nicholls in Somerset and owned by Clive Smith. He was known for his versatility and longevity, being the only horse ever to be top rated over 2 miles, 2.5 miles and 3 miles in the same season. He is also the first horse ever to win a Grade 1 race in six consecutive seasons, which he extended to seven. His Racing Post rating of 192 is the highest ever awarded to a National Hunt horse since those ratings began in 1987. He won the Cheltenham Gold Cup twice, in 2007 and 2009, becoming the first horse to regain the cup. In 2009, he beat Denman by thirteen lengths, after losing to the same horse by seven lengths the previous year. Kauto Star tried for three more years to win the race again, but the best placing he could achieve was third in 2011. He also won the King George VI Chase a record five times. Kauto Star was one of the most successful steeplechasers of any era: he finished his career with a National Hunt record of £3,775,883 in earnings, £2,375,883 of which was winner's prize money, a £1,000,000 bonus for the completion of the 2006/2007 Stayers Chase Triple Crown and a £400,000 reward for heading the BHA Table of Merit in the 2006/2007 season.

Kauto Star was foaled on 19 March 2000 and was bred by Mrs Henri Aubert. His sire was the Grand Prix de Saint-Cloud winner Village Star and his dam was Kauto Relka, who was a daughter of Port Etienne. Kauto Star is a half-brother to Kauto Stone, second in the 2011 Tingle Creek Chase, and Kauto Grand Mogol, who made his debut in 2012.

Kauto Star was initially trained in France by Serge Foucher at Senoble in the Mayenne region. He made his debut in a hurdles race at Bordeaux Le Bouscat Racecourse in France in March 2003, where he finished second. He started in two more hurdles races that season and won both. During the 2003/04 season, he raced over hurdles at Auteuil seven times and won twice. His last race of the season was the grade 3 Prix de Longchamp, which he won by 8 lengths. In France, he became known as 'L'Extraterrestre' (which translates to 'The Extraterrestrial')

Kauto Star first came to the attention of Paul Nicholls when he saw a video of him in action at Auteuil. Nicholls then sought to arrange a purchase through his bloodstock agent in France, Anthony Bromley. Nicholls arranged an owner in the shape of Clive Smith, who was looking to purchase a horse and had recently had a 500,000 guineas offer for another horse (Garde Champetre) outbid by J. P. McManus. He used 400,000 euro to purchase Kauto Star from his French owners.

Kauto Star moved to England for the 2004/05 season, and his first start of the season came in a class 3 novice chase race at Newbury, which he won easily by 9 lengths from Foreman, who went on to win the Maghull Novices' Chase the following season. His next start came in a class 3 novices' chase at Exeter. He started the 2/11 favourite in a field of three horses. Kauto Star took the lead after the eighth fence. He fell at the second to last fence when he had a 12 length lead. He was passed by Mistral De La Cour, but Kauto Star's jockey Ruby Walsh then re-mounted without his stirrups and chased the leader. He then hit the last fence, but still rapidly closed in on the finishing straight and lost out to Mistral De La Cour by a short-head. After the race, it was discovered that Kauto Star had sustained a fractured hock in the race, which ruled him out of the Cheltenham Festival and the rest of the season.

Kauto Star started the 2005/06 season in the Haldon Gold Cup at Exeter, where he finished in second place, four lengths behind Monkerhostin. He then started the 5/2 joint favourite for the Tingle Creek Chase. The previous season's Maghull Novices' Chase winner, Ashley Brook, was also at 5/2 and his Exeter conqueror, Monkerhostin, was at 9/2. Kauto Star went into the lead with three fences still to jump and held off Ashley Brook by 1+1⁄2 lengths. After this victory, he was sent off as the 2/1 favourite for the Queen Mother Champion Chase at the Cheltenham Festival in a field that included Moscow Flyer. Kauto Star fell at the third fence, and Newmill won the race.

Kauto Star started the 2006/07 season by easily winning the Old Roan Chase by 21 lengths from Armaturk. He next ran in the Betfair Chase, his first race over three miles. He took the lead at the last fence and drew clear to win by 17 lengths from multiple Grade 1 winner Beef Or Salmon. Two weeks later, he returned to racing over two miles in the Tingle Creek Chase. After taking the lead with three fences left to jump, he again pulled clear to easily win by 7 lengths from Voy Por Ustedes. On Boxing Day he lined up as the 8/13 favourite for the King George VI Chase at Kempton Park. He was positioned near the front by Ruby Walsh and took the lead with three fences to jump. After drawing clear, he hit the final fence but still won by 8 lengths from Exotic Dancer. Kauto Star then won the Aon Chase over L'Ami by a neck.

His final race of the season came in the 2007 Cheltenham Gold Cup at the Cheltenham Festival, where, ridden by Ruby Walsh, he started the 5/4 favourite. Kingscliff and Beef Or Salmon led in the early stages of the race, with Kauto Star held up near the rear. He made progress through the field and was near the leaders with four fences left to jump. Walsh then asked him for an effort and he quickened to take the lead two fences from the finish. He hit the final fence, but stayed on strongly to beat Exotic Dancer by 2+1⁄2 lengths, with outsider Turpin Green another 2+1⁄2 lengths back in third place. By winning the Betfair Chase, King George and Gold Cup, Kauto Star won the Stayers Chase Triple Crown £1 million bonus. He also won the National Hunt Order of Merit for the 2006/07 season and finished as the top-rated chaser.