Monimus

Monimus (/ˈmɒnəməs/; Greek: Μόνιμος; 4th century BCE) of Syracuse, was a Cynic philosopher.
According to Diogenes Laërtius, Monimus was the slave of a Corinthian money-changer who heard tales about Diogenes of Sinope from Xeniades, Diogenes' master. In order that he might become the pupil of Diogenes, Monimus feigned madness by throwing money around until his master discarded him. Monimus also became acquainted with Crates of Thebes.
He was famous for saying that "everything is vanity" (τῦφος, tuphos, literally 'mist' or 'smoke'). According to Sextus Empiricus, Monimus was like Anaxarchus, because they "compared existing things to a scene-painting and supposed them to resemble the impressions experienced in sleep or madness." He said that "it was better to lack sight than education, because under the first affliction, you fall to the ground, under the latter, deep underground," and he also said that "Wealth is the vomiting of Fortune."
He wrote two books: On Impulses, and an Exhortation to Philosophy, and he also wrote some jests mixed with serious themes (presumably related to Cynic-style spoudogeloia).
In book two of Marcus Aurelius' Meditations, he writes:

"There are obvious objections to the Cynic Monimus' statement that 'things are determined by the view taken of them'; but the value of his aphorism is equally obvious, if we admit the substance of it so far as it contains a truth"

Alternate translation by George Long revised by Classics Club editors, copyright 1945:
"Section II -15. Remember that all is but opinion. For what the Cynic Monimus said is obvious: and obvious too is the use of what he said, if a man accepts what may be got out of it only as far as it is true."