Its placing at the apex of British life is itself a little nuts, as the Ovation series shows.
You thought that LeBron James had already reached the apex of cultural relevancy?
But the KKK actually reached its apex of influence during the 1920s.
c.1600, from Latin apex "summit, peak, tip, top, extreme end;" probably related to apere "to fasten, fix," hence "the tip of anything" (one of the meanings in Latin was "small rod at the top of the flamen's cap"), from PIE *ap- "to take, reach." Proper plural is apices.
apex a·pex (ā'pěks)
n. pl. a·pex·es or a·pi·ces (ā'pĭ-sēz', āp'ĭ-)
The pointed end of a conical or pyramidal structure.