One of the oldest combat sports in the world is boxing. It is a sport that requires padded gloves in the ring, and two boxers (people who contest boxing fights) attempting to hit each other.

Boxing can be won by a variety of different means. One is a knockout when a fighter is caught and lies to the ground and cannot get up in 10 seconds. Without many rules and their complexities varying from age to period, boxing is perhaps the most difficult sport to assess dominance.

Mike Tyson, Joe Louis, and of course Muhammad Ali are some of the legendary heavyweight boxers in history. Yet there have still been fantastic fighters in all divisions. Let's find out the Top 11 Boxers of All-Time.

11. Henry Armstrong

Henry Armstrong of the USA during a fight. (Wikipedia)

From November 1937 to August 1938, Armstrong's nine months winning run is touted as one of the longest in all sports. In 1937 he went 27-0, capturing the featherweight title, with 26 knockouts. The next year the unrelenting intruder claimed the lightweight title after beating Barney Ross.

Most thought that he deserved to win the 1940 draw for the midweight crown. Nevertheless, he defeated 16 champions and recorded 19 welterweight title defenses.

10. Sugar Ray Leonard

Sugar Ray Leonard attends 2016 Charity Boxing Night. (Getty)

Wilfred Benitez, Roberto Duran, and Thomas Hearns gave Leonard a career commitment moments before he was 26. Leonard is generally regarded as one of the best boxers ever.

He captured world championships in 5 weight classes, a three-weight linear championship, and a welterweight title in his 20-year career. In addition to that, he was the first boxer to gain more than $100m, and he was recognized as the Boxer of the Decade in the 1980s.

9. Bernard Hopkins

Bernard Hopkins gestures to the crowd before a weigh-in in 2004. (Getty)

Bernard Hopkins has won numerous world championships in medium weight and lightweight in the course of his 28-year career, from 1988 to 2016. In 2004, Hopkins becomes the first male boxer to hold joint universal titles in all four primary boxing penalties when he beat Oscar De La Hoya in the WBO.

In 2011, when he captured a lightweight title, the age of 46, he became the oldest boxer in history to have won a world championship.

8. Joe Louis

Joe Louis in training for the fight against Jersey Joe Walcott in 1947. (Getty)

Joe Louis was a heavyweight champion from 1937 to 1949. One of the first dark-skinned champions who gained national status in the United States with his win over the German Max Schmeling in 1938. He defended his title 25 times during that time to become the world's longest-time heavyweight boxing champion.

In 1942, he became a private member of the military and until his discharge in 1945, when he rose to the rank of sergeant. In 1993, he was honored by the United States, becoming the first boxer to do that.

7. Rocky Marciano

Rocky Marciano removes their jackets on stage during a variety show during the 1950s. (Getty)

Rocky Marciano is the first boxing history heavyweight champion who retired with an intact record of no defeats. He ended his career with a record of 49-0 and 43 knockouts.

Regularly among the top lists of all time, he has 87.76 percent of deadly knockouts, which is one of the largest in the history of heavyweight boxing. In 1959, Marciano considered coming out of retirement, but that never happened.

6. Carlos Monzon

Carlos Monzon of Argentina poses for a picture. (Getty)

Monzon was the unchallenged middleweight champion for seven years prior to being sentenced to 11 years imprisonment in 1988 for the murder of his wife, Alicia Muniz. In spite of his very scandalous private life, he remains one of the most powerful middleweights in history.

Over the course of his career, he recorded 59 knockouts. The Argentine died in a tragic traffic accident in 1995.

5. Manny Pacquiao

WBA welterweight champion Manny Pacquiao poses on the scale during his official weigh-in. (Getty)

Despite being still active at the age of 42, Manny Pacquiao has fought some of the sports' most iconic fights in the ring. He beat Oscar De La Hoya in 2008, then in under six minutes, he swept away Ricky Hatton n 2009, and then several months later, the Philipines star won against Miguel Cotto.

In the "Fight of the Century" in 2015, Pacquiao lost to Mayweather. The longevity of Pacquiao and his unmatched climb have given the sport an iconic mark.

4. Mike Tyson

Mike Tyson speaks onstage during the Mike Tyson Undisputed Truths panel discussion. (Getty)

Mike Tyson, who won his first 37 career fights before finally losing to Douglas, was the youngest ever heavyweight champion in 1990. He was convicted of rape in 1992, and he served his sentence for three years.

Upon his return, he won two championships but then lost to Evander Holyfield and Lennox Lewis. Tyson is one of the most successful boxers ever, but his inability to win against other popular opponents hurts his overall reputation.

3. Sugar Ray Robinson

Sugar Ray Robinson of the USA prepares for a fight. (Biography)

Robinson went 85-0 as an amateur with 69 knockouts wins, 40 of those in the first round. At the age of 19, he became a professional in 1940, and come 1951, he had a record of 128-1-2 with 84 knockouts.

From 1946 to 1951, he was the world champion, and in the final year, he captured the middleweight title. In 1952, he retired, but then just two and a half years later, he came back and won the middleweight title.

2. Floyd Mayweather Jr.

Floyd Mayweather Jr. celebrates his victory in the WBC welterweight title. (Getty)

Floyd Mayweather Jr, who is one of the most talented boxers in the modern era, is yet to lose a fight in his career. He holds the record of 50-0, with 27 of them won by knockouts.

He has won world titles in five different weight divisions and is not only one of the biggest defenders ever but also the most accurate. From 2012 to 2015, Forbes ranked him as the world's most earning athlete.

1. Muhammad Ali

Muhammad Ali looks on during a bout in 1991. (Getty)

Ali ridiculed his rivals openly, arrogantly, called himself the "greatest”, but he always let his acts follow his words in the boxing ring. He was was one of the finest heavyweights boxers ever.

In the 1960 Olympics, he was the first fighter to lift the heavyweight title three times. With a record of 56-5 with 37 knockouts, Ali ended his career. His most renowned battles were the ones against George Foreman in 1974, and Joe Frazier, in 1975.