Leonhard Summer was born in Weiler, Feldkirch, Vorarlberg, Austria. He with his brothers John, Louis, Charles and Joseph were pioneer brewers in Denver and later in the mining boom towns in the mountains of Colorado.

The brothers emigrated to Dubuque, Iowa in the 1860s where they learned the brewing trades. By 1869 they had moved to Denver, where Leonhard and John operated the One Horse Brewery for a few years. By 1874 John and Louis moved on to Georgetown. Leonard and Joseph moved to Fairplay to take over the brewery started by Charles.

By 1880 the success Leonhard enjoyed began to ebb. Fires destroyed the Fairplay brewery twice. In 1883 his brother Joseph took his own life. In 1886 Leonhard and his wife Louisa were divorced. The panic of 1893 took another financial toll. The end came for Leonhard Summer came September 10, 1900 when he took his own life with a bullet to the brain. He was just shy of 62 years of age.