Jonathan Peacock was born in England. Peacock worked for Lill & Diversey in Chicago then made west to Rockford and established his own enterprise in 1849. The brewery he founded would survive him by nearly 50 years.

John V. Petritz was born in Austria.  He came to America in around 1870 and travelled west to Montana.  There he amassed a small fortune as a hotelier and saloonkeeper in the goldfields, even partnering for a time with future Olympia Brewery founder Leopold Schmidt.  In 1899 Petritz moved back east to Illinois, and at age 46 purchased the Peacock brewery in Rockford after the owners Edward and Frank Peacock died from Tuberculosis.  He invested $100,000 expanding and refitting the firm, and renamed it the Rockford Brewery.

Prohibition was closing in, however, and Petritz found himself on the other side of the ever-tightening law.  He was sued by the City and the county in a 2300 count indictment presided over by Federal Judge Kenesaw Mountain Landis.  The government won and Petritz's license was not renewed.  The Rockford Brewery entered Prohibition in 1918 and the rest of the state of Illinois followed two years later.  John V. Petritz died on The 2nd of February, 1930 at age 77.

Upon repeal the Rockford Brewery reopened, managed by Petritz's son John G.  It debuted Pet Ritz Beer as an homage to the family name.  It was brewed in Chicago and bottled in Rockford.  But competition was tough and the law was wary of the Petritz family.  The younger Petritz sold the family brewery in 1937 and it was renamed the Rock River Brewery.  The firm closed just four years later, never again to reopen.

This biography is in part borrowed from a nice anonymous write-up at findagrave.com