| Frederick IX | |
| Margrave of Brandenburg | |
| House: | Hohenzollern |
| Father: | John George, Elector of Brandenburg |
| Mother: | Elisabeth of Anhalt-Zerbst |
| Birth Place: | Cölln |
| Death Place: | Słońsk |
| Burial Place: | Parish church of Küstrin |
Frederick IX of Brandenburg (22 March 1588 in Cölln – 19 May 1611 in Sonnenburg, Prussia (now Słońsk, Poland)) was a Margrave of Brandenburg.
Frederick, a member of the house of Hohenzollern, was a son of the Elector John George of Brandenburg (1525–1598) from his third marriage to Elisabeth (1563–1607), daughter of Prince Joachim Ernest of Anhalt. Frederick was educated in Frankfurt and Tübingen and undertook an extensive Grand Tour through Europe.
In 1594, he was appointed Coadjutor and then, in 1610, elected Herrenmeister (literally, "Master of the Knights", equivalent to Grand Master) of the Order of Saint John, Bailiwick of Brandenburg, which was seated at Sonnenburg. He died at the age of 23 and was buried in the parish church of Küstrin.
His motto was Latin: Justus ut palma floredit (The righteous shall flourish like a palm tree).[1]