Alauddin Ri'ayat Syah al-Kahar was the third Sultan of the Aceh Sultanate, reigning from either 1537 or 1539 until his death. He is considered to be one of the strongest rulers in the history of the sultanate and greatly strengthened Aceh. Alauddin's reign was marked by increased conflict with his Portuguese and Malay rivals and his dispatching of envoys to the Ottoman sultan, Suleiman the Magnificent in the 1560s.

The Sultanate of Aceh, officially the Kingdom of Aceh Darussalam, was a sultanate centered in the modern-day Indonesian province of Aceh. It was a major regional power in the 16th and 17th centuries, before experiencing a long period of decline. Its capital was Kutaraja, the present-day Banda Aceh.