The Red Guards were militant Maoists dedicated to upholding the revolutionary line of Chairman Mao Zedong against the perceived "capitalist roaders" in the Chinese Communist Party, notably Deng Xiaoping and Liu Shaoqui. (Incidentally, given Deng's coup and subsequent "reforms" after Mao's death, converting China into a capitalist police state, it seems Mao wasn't wrong either)
The "Great Proletarian Cultural Revolution", as it came to be known, lasted 10 years in all, from 1966 - 1976 until Mao's death. However it's most active years were from 1966 - 1969. This period is still remembered and inspired revolutionary Maoists in Nepal, India and, in particular, the 'Shining Path' in Peru.
This two part documentary looks at the Red Guards and features film and images of rallies in Tiannemen Square and the main protagonists, including Mao, Lin Biao, and Madame Mao Jiang Quing.
Despite it's excesses and flaws, the Cultural Revolution nonetheless remains an example of upholding Marxism in the face of internal threats to the revolution. Long live MLM!!