Otto, known as the Merry, was Duke of Austria and Styria from 1330, as well as Duke of Carinthia from 1335 until his death. A member of the House of Habsburg, he ruled jointly with his elder brother Duke Albert II.

The Duchy of Styria was a duchy located in modern-day southern Austria and northern Slovenia. It was a part of the Holy Roman Empire until its dissolution in 1806 and a Cisleithanian crown land of Austria-Hungary until its dissolution in 1918.