A person who appears to have power but is in reality ineffectual.
This expression became known in the West as a slogan that Mao's Chinese communist state used against their opponents, particularly the US government. It appears as one of the quotations, or as he preferred to call them 'supreme directives' in the Quotations from Chairman Mao Zedong - better known as The Little Red Book, first published in 1964:
"Imperialism and All Reactionaries Are Paper Tigers"
Mao didn't coin the phrase; it had been an idiom in the Chinese language for some time. The first time it is recorded in print in English is in Sir John F. Davis' book The Chinese, 1836:
"A blustering, harmless fellow they [the Chinese] call 'a paper tiger'."