He could change more abruptly than a chameleon...whether Alcibiades found himself in the company of good men or bad, there was nothing he could not imitate and no habit he could not acquire. In Sparta, he took exercise, lived frugally, and wore a frown on his face; in Ionia he was fastidious, companionable, and easy-living; in Thrace he went in for hard drinking and hard riding; when he was with the satrap Tissaphernes he outdid the Persians, for all their magnificence, with his pomp and extravagance. It is not that he actually changed personality so readily, or that his character was infinitely mutable, but that when his real self was going to upset the people he was with, he assumed and took refuge in whatever appearance and image was appropriate for them.
— Plutarch, Parallel Lives: Life of Alcibiades
Octavianus entered, changing colour continually, like a chameleon, turning now pale now red; one moment his expression was gloomy, sombre, and overcast, the next he unbent and showed all the charms of Aphrodite and the Graces. Moreover in the glances of his eyes he was fain to resemble mighty Helios, for he preferred that none who approached should be able to meet his gaze...what a changeable monster is this! What mischief will he do us?
Emperor Julian the Apostate, from The Caesars one of his satires.