There have been thousands of thoroughbred horses that have raced, but which one stands out the most in your memory and the best ever?
Ther Is Two Many To Name.
Colin
A true rarity in racing, an unbeaten horse, Colin won all his 15 starts in 1907 and 1908, including the Belmont Stakes.
Exterminator
Beloved under the nickname "Old Bones," Exterminator originally was purchased as a workmate for Sun Briar, but wound up defeating the other horse in the 1917 Kentucky Derby. Exterminator won 50 of 100 races over eight seasons.
Man o' War
Although he last raced in 1920, Man o' War is still often regarded as the greatest of American race horses. He won 20 of 21 starts, often in record times and by commanding margins, and later became a great tourist attraction as a stallion.
Equipoise
Nicknamed "The Chocolate Soldier" for his rich coat color and extraordinary handsomeness, Equipoise raced through the age of seven in the 1930s, winning 29 of 51 races, often carrying top weights in handicap races.
Count Fleet
The Triple Crown winner of 1943, Count Fleet won the Belmont Stakes by 25 lengths in the final race of his career.
Citation
Winner of 19 races in 20 starts as a three-year-old in 1948, Citation followed Whirlaway as the second Triple Crown winner for the famed Calumet Farm. At six, he became the first Thoroughbred to reach $1 million in career race earnings.
Native Dancer
Early in the television era, the flashy "Gray Ghost" became a public idol. He won 21 of 22 starts, losing only to Dark Star in the 1953 Kentucky Derby.
Kelso
The only horse in history to be voted Horse of the Year five times, Kelso, reigned from 1960 through 1964. He was a great weight carrier and won five runnings of The Jockey Club Gold Cup, then raced at two miles.
Secretariat
In 1973, Secretariat became the first horse in a quarter-century to win the Triple Crown. His climactic moment was his 31-length victory in world record time in the Belmont Stakes. "Big Red's" image graced the covers of Time and Newsweek, as well as Sports Illustrated.
Forego
Over his brilliant six year career, Forego was awarded a record eight Eclipse Awards including Horse of the Year in 1974, 1975 and 1976, Champion Handicap Horse in 1974, 1975, 1976 and 1977 and Champion Sprinter in 1974. In his 54 career starts he only finished out of the money seven times. Forego is buried at the Kentucky Horse Park, near the Hall of Champions where he spent sixteen years delighting race fans.
Seattle Slew
In 1977, Seattle Slew became the first undefeated winner of the Triple Crown and was named Horse of the Year. The following year, Slew would firmly establish himself as one of the greatest champions of the 20th century by winning against 1978 Triple Crown winner Affirmed and England's top horse, Excellor.
Affirmed
In racing's greatest ongoing rivalry, Affirmed and Alydar waged war through 1977 and 1978. Affirmed won seven of their 10 meetings, including all three Triple Crown races, but most were extraordinarily close finishes.
Cigar
During one phase of his career, over three seasons, 1994-96, Allen Paulson's Cigar won 16 consecutive races, matching the modern record of Citation. He traveled to Dubai to win the first running of the Dubai Cup, and his career earnings were within $100 of $10 million. Cigar is now a resident of the Kentucky Horse Park's Hall of Champions.

secretariat
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red rum
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seabiscut
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Ther Is Two Many To Name.
Colin
A true rarity in racing, an unbeaten horse, Colin won all his 15 starts in 1907 and 1908, including the Belmont Stakes.
Exterminator
Beloved under the nickname "Old Bones," Exterminator originally was purchased as a workmate for Sun Briar, but wound up defeating the other horse in the 1917 Kentucky Derby. Exterminator won 50 of 100 races over eight seasons.
Man o' War
Although he last raced in 1920, Man o' War is still often regarded as the greatest of American race horses. He won 20 of 21 starts, often in record times and by commanding margins, and later became a great tourist attraction as a stallion.
Equipoise
Nicknamed "The Chocolate Soldier" for his rich coat color and extraordinary handsomeness, Equipoise raced through the age of seven in the 1930s, winning 29 of 51 races, often carrying top weights in handicap races.
Count Fleet
The Triple Crown winner of 1943, Count Fleet won the Belmont Stakes by 25 lengths in the final race of his career.
Citation
Winner of 19 races in 20 starts as a three-year-old in 1948, Citation followed Whirlaway as the second Triple Crown winner for the famed Calumet Farm. At six, he became the first Thoroughbred to reach $1 million in career race earnings.
Native Dancer
Early in the television era, the flashy "Gray Ghost" became a public idol. He won 21 of 22 starts, losing only to Dark Star in the 1953 Kentucky Derby.
Kelso
The only horse in history to be voted Horse of the Year five times, Kelso, reigned from 1960 through 1964. He was a great weight carrier and won five runnings of The Jockey Club Gold Cup, then raced at two miles.
Secretariat
In 1973, Secretariat became the first horse in a quarter-century to win the Triple Crown. His climactic moment was his 31-length victory in world record time in the Belmont Stakes. "Big Red's" image graced the covers of Time and Newsweek, as well as Sports Illustrated.
Forego
Over his brilliant six year career, Forego was awarded a record eight Eclipse Awards including Horse of the Year in 1974, 1975 and 1976, Champion Handicap Horse in 1974, 1975, 1976 and 1977 and Champion Sprinter in 1974. In his 54 career starts he only finished out of the money seven times. Forego is buried at the Kentucky Horse Park, near the Hall of Champions where he spent sixteen years delighting race fans.
Seattle Slew
In 1977, Seattle Slew became the first undefeated winner of the Triple Crown and was named Horse of the Year. The following year, Slew would firmly establish himself as one of the greatest champions of the 20th century by winning against 1978 Triple Crown winner Affirmed and England's top horse, Excellor.
Affirmed
In racing's greatest ongoing rivalry, Affirmed and Alydar waged war through 1977 and 1978. Affirmed won seven of their 10 meetings, including all three Triple Crown races, but most were extraordinarily close finishes.
Cigar
During one phase of his career, over three seasons, 1994-96, Allen Paulson's Cigar won 16 consecutive races, matching the modern record of Citation. He traveled to Dubai to win the first running of the Dubai Cup, and his career earnings were within $100 of $10 million. Cigar is now a resident of the Kentucky Horse Park's Hall of Champions.
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I did not have a chance to see Affirmed or Secretariat evn Red Rum race but I have seen Cigar, Makybe Diva (double Melbourne Cup winner) and Smarty Jones.
I think it is Cigar.
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Btw I think this one of the few excellent questions that are posted. A good question is one that brings out strong and usually passionate emotions.
The best one is an Australian horse Pharlap… Google it and read his history. Truly amazing.
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My racehorse-TWO HONEST…He won the New Jersey Knickerbocker in 1992.
On an impersonal note:
The greatest colt/horse = Kelso
The greatest filly = Ruffian
The greatest jockey = Eddie Arcaro (rode 2 Triple Crown champions-Citation/Whirlaway). The combination of Kelso and Arcaro was the height of two great champions coming together.
The greatest trainer = James Fitzsimmons (trained 2 Triple Crown champions-Omaha/Gallant Fox)
Perhaps a little more than you asked for, but, I couldn't resist…
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Nijinsky, Arkle,
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Eclipse. He raced in GB 1769 -1770. He was named as he wan born during the solar eclipse of 1764
He retired mainly because no one wanted to race their horses against him. He went through his career unbeaten (18 races), and won by such huge distances that the phrase "Eclipse first, the rest nowhere." was used.
He was a huge success at stud and The Royal Veterinary College have recently determined that 80% of all racehorses today have Eclipse somewhere in their pedigree
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http://en.wikipedia.org/wiki/Eclipse_(horse)
Certainly Secretariat, because as one fella said, no horse ever made could have beaten him on June 9, 1973 when he won the Belmont Stakes by 31 lengths.
TvNB
Man O’WAR! HE was the “biggest and the bestest”!
Kincsem
(foaled 1874), European racehorse whose total of 54 victories (1876–79) without defeat was into the 1980s the best unbeaten record in the history of flat (Thoroughbred) racing. A mare sired by Cambuscan out of Water Nymph (both English-bred horses), she was foaled in Hungary and raced in Austria, England, France, and Germany, as well as in her native country.
http://www.britannica.com/EBchecked/topic/318027/Kincsem
There’s a good case for Phar Lap, an Australian horse with 51: 37-2-3 and 9 unplaced. Unfortunatley he was poisoned by some one in the US when he visited. Some say the mafia. See some of the weight he carried in G1 races, unbelievable!
http://en.wikipedia.org/wiki/Phar_Lap