Based on this passage, why is Chris Kuroda's nickname CK5?

Chris Kuroda, who has been Phish's lighting director since 1989, creates elaborate light displays during the band's concerts that are sometimes improvised in a similar fashion to their music.[266][267] Justin Taylor of The Baffler wrote, "You could hate this music with every fiber of your being and still be ready to give Chris Kuroda a MacArthur "genius" grant for what he achieves with his light rig."[267] Kuroda is often referred to by fans as the unofficial fifth member of the band, and has been given the nickname "CK5".[268]

Chris Kuroda's nickname, CK5, adds the number 5 to his initial. That is because his improvised light shows during Phish concerts give him a role comparable to a fifth member of the band.