The surname Friz derives from Fritz, diminutive of the German name Friederich (Frederick), originating from the Old Germanic Frithurik, composed of the prefix frithu ("peace", "friendship": Friede, in German) and the suffix rikia ("lord", "prince"), meaning "Lord of Peace", "The One who assures peace".
The surname is diffused in the Adige Valley in northern Italy. It's a German surname which established originally in the Region of Trentino on the comune di Garniga (town of Garniga)."
"Der Alte Fritz" refers specifically to Frederick the Great.
Source: "Saggio di Commento ai Cognomi Tridentini", by Ernesto Lorenzo, 1895.