Wilhelm Peter Mathias Rahr was born in Prussia.  He was a trained brewer in his native land.   He emigrated to America in 1847 and established himself in his profession in the town of Manitowoc, Wisconsin.  In 1849 Wilhelm married Natalia Geselschap, a fellow Prussian emigre.  Over the next ten years they would have six children.

The 1860 census shows Rahr as having two brewers on staff, Franz Koepel and Nicolas Raeder.  By 1880 he brought his sons in as partners.  William Sr. was the brewer, while brothers Reinhardt and Max went into the malting business.  

Wilhelm Peter Mathias Rahr died on October 5th 1880 at the age of 67.  The brewery continued with family management until 1920 when it was closed down by National Prohibition.