What is a brief history on the idea that the Pope is the Antichrist? I am quite familiar with the Reformers' opposition to the Papacy, and many said the Pope is the Antichrist. What confuses me is this quote from that same page:

In calling the pope the &quot;antichrist,&quot; the early Lutherans stood in a tradition that reached back into the eleventh century. Not only dissidents and heretics but even saints had called the bishop of Rome the &quot;antichrist&quot; when they wished to castigate his abuse of power.

I was under the impression that the idea originated with the Reformers; however, it clearly did not. I would like a brief history of this idea up until the Reformers.
This answer draws extensively from Angel Pope and Papal Antichrist, Bernard McGinn, Church History 47(2):155-173, 1978. McGinn is a Catholic and an expert on medieval mysticism.

The identification of the Pope with the Antichrist of Revelation comes essentially from Joachim of Fiore, a twelfth-century mystic who was particularly interested in the pattern of history. His theology was condemned in a synod of 1260, though it was very influential - firstly, among groups in the Church who were devoted to lives of poverty, especially the Franciscans, and secondly among various schismatic the-end-of-the-world-is-nigh sects. 

For Joachim and followers, contemporary power struggles over the nature of the papacy, and questions over legitimacy during periods where there were antipopes, foreshadowed a future apocalyptic showdown between a pastor angelicus, novus dux, or orthopontifex (the good guy) and an Antichrist or pseudopontifex (the bad guy).  This was a divergence from previous Antichrist theories, which tended to think he would be a (Holy) Roman Emperor.1 Joachim himself may or may not have thought that the Antichrist would be a "proper" elected pope, as opposed to someone setting himself up in mockery of the true church. He did think that the result of the conflict would be the beginning of a new era, where all people would live a simple, monastic, contemplative life, and where there would no longer be a church or pope. 2

The next generation of Joachimites certainly did believe in the pseudopontifex. From them come the Dulcinians and other millenarian sects. By the way, if you've read Umberto Eco's The Name of the Rose, then you've met some of these people! Part of the problem for the Franciscans in that book is that everyone assumes they're Dulcinian. Both groups were influenced by Joachim, but people like William of Ockham stayed within the Church, while trying to promote poverty and simplicity in life, and did not want to get rid of the papacy. Even Ubertino of Casale, who called Boniface VIII and Benedict XI a pair of antichrists, didn't want anything more than to have a better pope take over.3

There is an influence on the Lollards, whose founder John Wycliffe (1330-1384) had similar views of the papacy. And from these "proto-Reformers" it is a hop, skip and jump to the actual Reformation, similarly animated by concern about the church being wealthy and corrupt. The big difference, roughly from Wycliffe onwards, was that now the institution of the papacy itself was seen as Antichrist - unlike the classical Joachimite view of a good and a bad pope fighting it out. For the Protestants there could not be a good pope! All popes, for them, were like mini-antichrists preparing the way for the final Antichrist of Revelation (the antichristus magnus). In a previous answer of mine you can find some references to Luther, Calvin, etc., discussing this idea.

Now, there have been other people, even before Joachim of Fiore, who used the word "antichrist" in relation to some pope. But these occurences are fairly sporadic and not influential. McGinn cites Arnulf (an archbishop of Reims), speaking at the synod where he was deposed in 991, calling John XV "Antichrist seated in the temple of God and showing himself as if he were God".4 Any stuff like this is just name-calling, and in any case is invariably about some specific individual pope, not the institution of the papacy or the hypothesized pseudopontifex.

In summary, the Pope-Antichrist link is in its purest form a creature of the Reformation, where the very institution of the papacy was held to be intrinsically evil. This built upon an earlier trend of criticizing the church for some combination of wealth, lack of zeal, or political disagreement: and where people looked forward to either a better pope, or the coming of a messianic golden age where the whole question was moot. The people associated with this view were necessarily "dissidents", and sometimes "heretics". I have not found any of them who are accounted "saints", and frankly I think it rather unlikely (unless we mean "saints" in a much more general sense). 

1. See eg Hugh of Newcastle, De victoria Christi contra Antichristi (1319), or the Ludus de Antichristo, a mid-12th century play about an imperial Antichrist.
2. Antichrists and Antichrist in Joachim of Fiore, Robert E. Lerner, Speculum 60:3, 1985.
3. Arbor vitae crucifixae Jesu, Ubertino of Casale (1305) at 5.8 and 5.11 (f. 230rb-233ra, 237vb in the Venice 1485 printing).
4. Acta concilii Remensis ad Sanctum Basolum, Gerbert of Aurillac (aka, later, Pope Sylvester II), in Monumenta Germaniae Historica, Scriptores 3, 672.