Background
Otto was a son of Duke Otto II of Brunswick-Harburg (1528-1603) from his second marriage, with Hedwig (1535-1616), the daughter of Cont Enno II of East Frisia.
Otto was a son of Duke Otto II of Brunswick-Harburg (1528-1603) from his second marriage, with Hedwig (1535-1616), the daughter of Cont Enno II of East Frisia.
Their joint reign was described as harmonious. On 14 April 1621 in Wolfenbüttel, Otto III married Hedwig (1580-1657), the daughter of Duke Julius of Brunswick-Wolfenbüttel. This marriage remained childless.