Peter I or Peter Frederick Louis of Holstein-Gottorp was the Regent of the Duchy of Oldenburg for his incapacitated cousin William I from 1785 to 1823, and then served himself as Duke from 1823 to 1829.

The Duchy of Oldenburg named after its capital, the town of Oldenburg was a state in the north-west of present-day Germany. The counts of Oldenburg died out in 1667, after which it became a duchy until 1810, when it was annexed by the First French Empire. It was located near the mouth of the River Weser.