Who said "The man who does not do his own thinking is a slave."?

This quote is attributed to Mark Twain.

The man who does not do his own thinking is a slave. - Mark Twain

"The man who does not do his own thinking is a slave."

Mark Twain Freedom

Novelist American 1835–1910

"The secret of getting ahead is getting started."

"If you tell the truth, you don't have to remember anything."

"The man who does not read has no advantage over the man who cannot read."

"Kindness is the language which the deaf can hear and the blind can see."

"Freedom to pursue your passion is precious."

"Freedom comes at a cost."

"Order isn't restriction. It's freedom."

"Freedom comes with responsibility"