Dick Cheney. Not Rumsfeld. It wasn't original to Cheney either.
"There are known knowns" is a phrase from a response United States Secretary of Defense Donald Rumsfeld gave to a question at a U.S. Department of Defense (DoD) news briefing on February 12, 2002 about the lack of evidence linking the government of Iraq with the supply of weapons of mass destruction to terrorist groups.
Rumsfeld stated:
Reports that say that something hasn't happened are always interesting to me, because as we know, there are known knowns; there are things we know we know. We also know there are known unknowns; that is to say we know there are some things we do not know. But there are also unknown unknowns – the ones we don't know we don't know. And if one looks throughout the history of our country and other free countries, it is the latter category that tend to be the difficult ones.
He wasn't however the first one who used the phrase
The idea of unknown unknowns was created in 1955 by two American psychologists, Joseph Luft (1916–2014) and Harrington Ingham (1916–1995). They used it as a technique to help people better understand their relationship with themselves as well as others. It was also commonly used inside NASA.
And as you can see there is no mention of Dick Cheney
I heard it many times in corporate business discussions well before I heard it uttered by any government types.