Obviously there’s the glaring examples: Templars, Hospitallers and Teutonic Knights.
My question however is, was it a requirement to be a Christian to be a Knight? Was there ever a group of Pagan Knights? Or Agnostic Knights? Or any other religious or spiritual sect aside from Christian that has been historically recorded?
I'm sure more can said on the topic, but while we wait for an expert, this thread has some good answers from u/BookQueen13, u/Rittermeister, and u/Guckfuchs.