Born on June 5, 1882 in Copenhagen, Denmark. Was named Oscar Mathæus Nielsen. Emigrated to the United States the following year.

Active as a professional boxer from 1896 until 1917.

Held the World lightweight Championship in the periods 1905-1906 & 1908-1910. Won 6 of 9 title-fights.

At the end of his career he had a record of 59 victories (38 stoppage wins), 19 losses, 19 draws and 33 no-decisions. He was stopped only twice in 133 fights.

Died on February 7, 1954 - aged 71.

	Began his career as a prizefighter at 14 years of age by defeating Wallace's Unknown in a traveling circus.
	Won the World lightweight Championship by stopping Jimmy Britt in a rematch, and became the first Dane ever to win such a championship. Some authorities still recognize this bout as for only the 'white' championship with Joe Gans as the real title-holder.
	Had the first of three encounters with the great Joe Gans in 1906, and was disqualified in the 42nd round for hitting low. This is the longest world title-fight ever held under the Queensberry rules. Recieved $23,000 for this bout.
	Regained the championship in 1908 by stopping Joe Gans in the 17th round, and repeated the victory some two months later.
	Retained the title three times more before finally losing the championship in 1910 to Ad Wolgast. The referee stopped the contest in the 40th round in favour of Wolgast.
	Registered his first and only clean loss by kayo against Owen Moran, also in 1910.
	Continued his ring career until 1917. Met Ad Wolgast for the third time in 1913, and lost the newspaper decision.
	These credentials make The Durable Dane the greatest Danish-born fighter ever.