As a professional fighter Sullivan was nicknamed The Boston Strongboy.
As a youth he was arrested several times for participating in bouts where the sport was outlawed.
He went on exhibition tours offering people money to fight him.
Sullivan won more than 450 fights in his career.

There is some controversy among boxing historians over whether Sullivan had sparred with black boxer James Young at Schieffelin Hall in Tombstone, Arizona in 1882.
It is significant because Sullivan insisted that he never fought a black boxer.
 If it did occur, Sullivan possibly had a brief sparring session with the resident from Tombstone, and didn't regard it seriously as a bout.

In 1883–84 Sullivan went on a coast-to-coast tour by train with five other boxers.
They were scheduled to hold 195 fights in 136 different cities and towns over 238 days.
To help promote the tour, Sullivan announced that he would box anyone at any time during the tour under the Queensberry Rules for $250.
He knocked out eleven men during the tour.

In Sullivan's era, no formal boxing titles existed.
He became a champion after defeating Paddy Ryan in Mississippi City, near Gulfport, Mississippi on February 7, 1882.
Modern authorities have retroactively labelled Ryan the "Heavyweight Champion of America", but any claim to Ryan's being a "world champion" would have been dubious; he had never contended internationally as Sullivan had.

Depending on the modern authority, Sullivan was first considered world heavyweight champion either in 1888 when he fought Charley Mitchell in France, or in 1889 when he knocked out Jake Kilrain in round 75 of a scheduled 80-round bout.
Arguably the real first World Heavyweight champion was Jem Mace, who defeated Tom Allen in 1870 at Kenner, Louisiana, but strong anti-British sentiment within the mostly Irish-American boxing community of the time chose to disregard him.

When the modern authorities write of the "heavyweight championship of the world," they are likely referring to the championship belt presented to Sullivan in Boston on August 8, 1887.
The belt was inscribed Presented to the Champion of Champions, John L. Sullivan, by the Citizens of the United States.
Its centerpiece featured the flags of the US, Ireland, and the United Kingdom.

Mitchell came from Birmingham, England and fought Sullivan in 1883, knocking him down in the first round.
Their third meeting took place in 1888 on the grounds of a chateau at Chantilly, France, with the fight held in driving rain.
It went on for more than two hours, and by the end of the bout, both men were unrecognisable and had suffered so much damage that neither could lift their arms up to punch.
Both men couldn't continue and the contest was considered a draw.

At this point, the local gendarmerie arrived and arrested Mitchell.
He was confined to jail for a few days and later fined by the local magistrate, as bare-knuckle boxing was illegal in France at that time.
Swathed in bandages, Sullivan was helped to evade the law and taken across the English Channel to spend the next few weeks convalescing in Liverpool.
As a professional fighter Sullivan was nicknamed The Boston Strongboy. As a youth he was arrested several times for participating in bouts where the sport was outlawed. He went on exhibition tours offering people money to fight him. Sullivan won more than 450 fights in his career.
There is some controversy among boxing historians over whether Sullivan had sparred with black boxer James Young at Schieffelin Hall in Tombstone, Arizona in 1882. It is significant because Sullivan insisted that he never fought a black boxer.  If it did occur, Sullivan possibly had a brief sparring session with the resident from Tombstone, and didn't regard it seriously as a bout.
In 1883–84 Sullivan went on a coast-to-coast tour by train with five other boxers. They were scheduled to hold 195 fights in 136 different cities and towns over 238 days. To help promote the tour, Sullivan announced that he would box anyone at any time during the tour under the Queensberry Rules for $250. He knocked out eleven men during the tour.
In Sullivan's era, no formal boxing titles existed. He became a champion after defeating Paddy Ryan in Mississippi City, near Gulfport, Mississippi on February 7, 1882. Modern authorities have retroactively labelled Ryan the "Heavyweight Champion of America", but any claim to Ryan's being a "world champion" would have been dubious; he had never contended internationally as Sullivan had.
Depending on the modern authority, Sullivan was first considered world heavyweight champion either in 1888 when he fought Charley Mitchell in France, or in 1889 when he knocked out Jake Kilrain in round 75 of a scheduled 80-round bout. Arguably the real first World Heavyweight champion was Jem Mace, who defeated Tom Allen in 1870 at Kenner, Louisiana, but strong anti-British sentiment within the mostly Irish-American boxing community of the time chose to disregard him.
When the modern authorities write of the "heavyweight championship of the world," they are likely referring to the championship belt presented to Sullivan in Boston on August 8, 1887. The belt was inscribed Presented to the Champion of Champions, John L. Sullivan, by the Citizens of the United States. Its centerpiece featured the flags of the US, Ireland, and the United Kingdom.
Mitchell came from Birmingham, England and fought Sullivan in 1883, knocking him down in the first round. Their third meeting took place in 1888 on the grounds of a chateau at Chantilly, France, with the fight held in driving rain. It went on for more than two hours, and by the end of the bout, both men were unrecognisable and had suffered so much damage that neither could lift their arms up to punch. Both men couldn't continue and the contest was considered a draw.
At this point, the local gendarmerie arrived and arrested Mitchell. He was confined to jail for a few days and later fined by the local magistrate, as bare-knuckle boxing was illegal in France at that time. Swathed in bandages, Sullivan was helped to evade the law and taken across the English Channel to spend the next few weeks convalescing in Liverpool.
John L. Sullivan