Dorje Shugden is a Buddhist movement upset with the current Dalai Lama. An entire propaganda machine is poised to knock and villify Tibet's political and spiritual leader, courtesy of the imperial Chinese government trying to consolidate holdings such as Tibetan, Taiwanese, and Uighur land. The immense resources it is able to marshal against him far outweigh internal Buddhist opposition to the Dalai Lama. But the fact that it is a Buddhist movement is a substantive twist. This is the controversy in a nutshell:
Dorje Shugden is a deity in Tibetan Buddhism. Highly regarded in the Gelug school, he is considered a Dharma Protector or "guardian angel." The practice of venerating Dharma protectors is central to most practitioners of Tibetan Buddhism. Dorje Shugden is thought of as the incarnation of Gelugpa Lama Dragpa Gyaltsen of Drepung Monastery. He was a contemporary of the 5th Dalai Lama.
Dorje Shugden's enlightened nature has been debated since his appearance in the 17th century. With the current (14th) Dalai Lama's growing public opposition and subsequent "explicit ban" of the practice, this debate has escalated into what is known as the Dorje Shugden Controversy. While such a controversy is distressing to Vajrayana Buddhists, it is quite pleasing to Chinese military officials.