My major area of research is 15th century Germany, so believe me, I would love to claim Jan Hus as a more important historical actor than Luther. But it's just not true.

One very useful way to think of medieval Christianity over time is to consider it as waves of reform. They had different emphases, overlapped chronologically, and sometimes crashed and clashed into each other. Carolingian liturgical reform and semi-standardization, Cluniac reform at the monastic level, the 11th century Gregorian reforms of the papacy and non-monastic clergy, 12th century Cistercian monastic movement alongside some Cluniac houses shifting gears PLUS the eremetic (hermits!) movements and the beginnings of lay urban enthusiasm for living an all-around religious life, the great pastoral shift of the 13th century spearheaded by the Franciscans and Dominicans, the explosion of the women's religious movement/movements, &c &c.

What all these movement had in common--right down to Wycliffe and the "Lollards" in England and Hus and the Brethren in Bohemia--was the desire to reform the Church. They wanted to fix what they thought was broken in the Church based in Rome (sometimes Avignon) and headed by the pope.

At the Council of Constance, Hus was invited, betrayed, arrested, and horrifically executed for heresy. The papacy and the emperor determined to go to war to smash his now-declared-heretical followers.

But something unexpected happened: the Hussites won. But crucially for current purposes, they won in a very specific way. During the fighting, the Hussites split into more and less radical factions. The most moderate, the Utraquists, took their name from their belief that Communion in both kinds (bread and wine) must be offered to the laity, not just bread. This was not okay with the Church. However, the orthodox side made the strategic decision that it was best to ally with the moderates to defeat the radicals (Taborites and Waisen).

This alliance included the Church's acceptance of Utraquist beliefs within their own liturgical rite--and the Utraquists' acceptance of papal authority. So although the Brethren had their own thing going on in terms of worship services, they were part of the Church, the Church that continued to unite Latin Europe.

And this is what makes the Protestant Reformation different than every previous little-r reform movement. Luther and his followers broke the Church.

By all accounts, that wasn't his initial intention at all. The 95 Thesen was a dramatic text and its release date to the Archbishop of Mainz compounded that, but Luther's initial point was the abuses of the Church--not an inherently flawed theology. In fact, a lot of eventual-Protestant beliefs flow smoothly out of 15th century orthodox teaching. Luther spent a good portion of his life as an Augustinian monk and theology professor, after all! Some of the greatest influences til the end of his life remained 14th century (orthodox) mystic Johannes Tauler and Luther's mentor in the Augustinian order, Johannes von Staupitz.

It wasn't until the Leipzig Disputation that Luther played his full hand--or rather, that University of Ingolstadt rector Johann Eck walked Luther into saying Hus shouldn't have been burned--that is, that the Church erred in executing him. This triggered Exsurge Domine, the papal bull excommunicating Luther, and the Diet of Worms which pretty much formally branded him a heretic.

That's fine and normal; the Church had seen and survived intact many "heretical" movements before.

The key shift was probably 1523. That summer, the German Reichstag (parliament) declared that the 'Luther movement' represented not a heresy but a schism--a split of the Church into parts. The expectation was surely that the two sides would come to an eventual agreement and union. That's what had happened every previous time in Latin Christendom. (The 1054 East-West schism and the early Church councils split 'the Church,' but at the time the Church's political role and geographical divisions were a very different situation than it had grown to by the late Middle Ages).

Except...this time, it didn't. The funky politics of the Holy Roman Empire and the snowball effect of the Luther movement combined to secure "Protestant" beliefs an actual future--a future outside the Catholic Church.

Hus influenced Luther's theology and his life story has a key part to play in the unfolding of the early Reformation. However, on his own Hus' agitation won over some people to variations on his theology but they preserved the unity of the Church. Luther's agitation, in the end, split the Latin Church for good. It broke the legal and moral unity of Western Christendom.

Hus unquestionably matters, but in the long run, Luther's legacy is far greater.