Daniel 7:6 (BSB)

Next, as I watched, suddenly another beast appeared. It was like a leopard, and on its back it had four wings like those of a bird. The beast also had four heads, and it was given authority to rule.

From Daniel 7. Also in the ESV.

Commentary on Daniel 7:6

John Calvin (Reformed), Calvin's Commentaries on Daniel 7:6: Daniel has already spoken of two empires, namely, the Chaldean and Persian. Interpreters agree in the necessity for referring this vision to the Macedonian Empire. He compares this kingdom to a leopard, or, as some translate, a panther, since Alexander obtained his great power through swiftness alone; and although it is not by any means a striking animal, yet it managed by its remarkable speed...
Matthew Henry (Presbyterian), Matthew Henry's Complete Commentary on Daniel 7:1-8: The date of this chapter places it before ch. 5, which was in the last year of Belshazzar, and ch. 6, which was in the first of Darius; for Daniel had those visions in the first year of Belshazzar, when the captivity of the Jews in Babylon was drawing near a period.
John Gill (Reformed Baptist), Exposition of the Old and New Testaments on Daniel 7:6: After this I beheld, and, lo another, like a leopard,.... Another beast, another monarchy, a third monarchy succeeding the Persian monarchy, and which rose up on the ruins of that; Darius king of the Persians being beaten by Alexander king of Macedon, who was the instrument of setting up the Grecian monarchy here intended; compared to a leopard, a smaller creature than a lion; signifying...
Jamieson-Fausset-Brown (Reformed), Commentary Critical and Explanatory on the Whole Bible on Daniel 7:6: leopard--smaller than the lion; swift (Hab 1:8); cruel (Isa 11:6), the opposite of tame; springing suddenly from its hiding place on its prey (Hos 13:7); spotted. So Alexander, a small king, of a small kingdom, Macedon, attacked Darius at the head of the vast empire reaching from the Ã†gean Sea to the Indies.