The Koch brothers built their first fortune on the particularly dirty form of oil mined in Alberta's tar sands, where they have been major players for 50 years, and remain deeply invested.
The key moment came in 1969, when Charles Koch secured full ownership of a heavy oil refinery in Minnesota. Almost forty years later he called the acquisition "one of the most significant events in the evolution of our company."
Here is an interactive timeline that tells the story of the Kochs' 50 years in the tar sands. It updates an in-depth story InsideClimate News published in 2012.