As of 2024, how many legitimate Catholic popes have taken the name John?

Currently the accepted number of popes who used the name John is at 21, although the most recently pope named John was John XXIII (reigned 1958 – 1963). Numbering of the Catholic popes named John had some issues, the first 14 (John I through John XIV) did not have any controversy in the numbering. But medieval historians misread the “Liber Pontificalis” (or “Book of Popes”) and believed there was a Pope between John XIV and John XV who was also named John, giving a name “John XIV bis”, then finding later that pope didn’t exist.

The confusion continued when John XVI (papacy 997 – 998) was elected to oppose Pope Gregory V and John XVI is currently considered an antipope, but his number was kept in the sequence. The number 20 (XX) was skipped because when John XXI (1276 – 1277) selected his number, he believed John XV through XIX should have been XVI through XX. The most recent issue with numbering was John XXIII (1410 – 1415) who was listed as a legitimate pope until the mid-20th century. He was slated as an antipope and XXIII was reused by Angelo Roncalli who became Pope John XXIII in 1958.