"The black pope" is a nickname given to the Father General of the Society of Jesus.
https://www.catholic.com/qa/does-the-black-pope-wield-the-true-power-in-the-vatican
New general of the Jesuits: I do not like being called "the black pope"
https://www.romereports.com/en/2016/10/18/new-general-of-the-jesuits-i-do-not-like-being-called-the-black-pope/
A meaningful stance, as the General of the Jesuits is called the “Black Pope”, because his term of office lasts for the remainder of his life, and because he has unlimited powers, like the Pope.
http://www.mondayvatican.com/vatican/the-pope-black-and-white