David Bower is the most notable example. He was the executive director of the Sierra Club in the late 60s early 70s and was a strong supporter of the clubs "Atoms Not Dams" initiative to protect natural waterways.

Suddenly he became staunchly anti-nuclear and tried to create enough chaos to destroy the club. After failing to do so, he left to start a competing organization called Friends of the Earth that was anti-nuclear first environmentalism second. They went on to fund and facilitate protests and anti-nuclear action around the world.

It was later discovered he received half a million dollars (about $7m today) from the CEO of ARCO around the time all the trouble started.