I believe it was Eisenhower in 1954 that added the “under God” language in direct response to the communist threat.
No Knights of columbus involvment.
http://www.kofc.org/un/eb/en/news/legislative/detail/549399.html
From the official “Knights of Columbus” website....
The Knights of Columbus led the campaign to add the words under God to the Pledge in the early 1950s, and the trial court agreed to allow the Knights of Columbus to join the present case as defendants when it was originally filed in 2005.