There are known knowns are the opening words of a statement to the press made by Donald Rumsfeld in February 2002.
The above statement was made by Rumsfeld on February 12, 2002 at a press briefing where he addressed the absence of evidence linking the government of Iraq with the supply of weapons of mass destruction to terrorist groups. It was criticised as an abuse of language by, among others, the Plain English Campaign. However, linguist Geoffrey Pullum disagreed, saying the quotation was "completely straightforward" and "impeccable, syntactically, semantically, logically, and rhetorically."
As for the substance of his statement, Rumsfeld's defenders have included Canadian columnist Mark Steyn, who called it "in fact a brilliant distillation of quite a complex matter",