John Grün, who claimed to be the strongest man in the world, was born in Mondorf-les-Bains on August 27,1868, into a family of craftsmen and Yenish people (an indigenous, semi-nomadic group involved in trades like metalworking, basketry and entertainment), who were longtime residents in the town. 

Grün’s father was a blacksmith and wandering tinsmith and not wanting to take up that trade, John emigrated to the U.S. in 1889. While working in a St. Louis brewery, he met Aloysius Marx, a professional athlete, who after noticing how easily Grün moved beer barrels around, persuaded him to become part of a strongman partnership called “The Marx Brothers.” The duo drew crowds of enthusiasts wherever they appeared.

When Grün returned to Luxembourg in 1892, he became famous as the strongest man in the world. He performed his feats of strength in circuses, music halls and other venues throughout America and Europe. Known as the “Luxembourg Hercules,” his acts included tearing apart decks of cards and horseshoes, breaking a block of stone on his chest with a hammer and halting a moving car. It is said that no one else could lift blocks of iron as easily as Grün. Harry Houdini, who frequently performed with Grün, said that Grün “juggled hundreds and toyed with thousands of pounds as a child plays with a rattle.”

After a serious injury in 1909, Grün gave up his professional career and left America for London where he became the landlord of a public house. In 1912, he was stricken with a disease and died in Ettelbruck, Luxembourg, on November 3, 1912. 

Grün was said to be the first Luxembourg sportsman to perform abroad. In recognition of his feats, a monument of him was erected in his native Mondorf-les-Bains.