The phrase "black knight" refers to a person or entity who defends a cause or fights for someone else, even when it is difficult or unpopular. It is a metaphor for someone who fiercely protects and supports others. Full definition
Non-western influence remained by and large outside their analysis, although they did concede a category of black knights. (blog.politics.ox.ac.uk)
Oh, did I mention, there's a giant black knight that will spawn every once in a while, and start wailing on your walls? (playstationlifestyle.net)
The publishing gatekeepers with their secret handshakes and lofty glares remind me of the black knight in «Monty Python and the Holy Grail.» (redeeminggod.com)