Alexander the Great was a king of ancient Macedon.
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history
A pupil of 亚里士多德, he conquered the Persian Empire and Egypt and reached India in about ten years, founding many cities named after himself, the most famous being 亚历山大港 in Egypt.
usage
大帝 'great emperor' after a ruler's name is the Chinese for 'the Great': 彼得大帝 is Peter the Great. On its own, 亚历山大 is just the name Alexander.