The head of certain churches is known as the Pope: see  for complete list.
Links on Althistory Wiki
Roman Catholic Church
- List of Popes of Papal States (Washington Shot at Murdering Town!)
- List of popes (Cabotia and Brasil)
- Benedict XV - KuK Franz Joseph's imposition of the papal veto is not applied, and Cardinal Mariano Rampolla is elected Pope in 1903.
- Pope John Paul II (Lauerdauch World)
- Pope Augutta (Lauerdauch World)
- John Paul II (Basil Hume)
In OTL there have been a number of persons designated Antipopes - who were in opposition to the Pope in Rome.
In the present era a number of Catholic figures, often of a more conservative frame of mind have declared the See of Rome vacant, and have set themselves up as Popes: they are usually known as sedevacantists, and often have a fairly minor support.
There are various althistory possibilities arising - for example the various Antipopes were recognised as the true pope. Alternatively the Antipope and Sedevacantists gain enough support to form recognisable 'breakaway Catholic churches' (as outsiders might so define them.)
More general possibilities
Presently only cardinals under 80 can vote in a Conclave: it would be possible, if a relatively young Pope were incapacitated for a long period of time that upon his death that there would be no competent cardinals.
There appears to be no procedure for a Pope who adopted positions that were genuinely heretical, or who becomes incapable of ruling through physical incapacity or mental incompetence.