I wouldn't call Qutb a reformer, I would call him a radical, and there is a big difference. Youssef Choueiri in his book Islamic Fundamentalism separates fundamentalism into "reformist" and "radicalist" elements - the reformers sought to transform institutions and society as they stood, while the radicals sought to overturn existing institutions and make new ones from the ground up. While they're still part of the same overall ideology, the methods are very different and worth noting.
In this context, Martin Luther was a reformer; Joseph Smith was a radical. Martin Luther wanted to reform the Christian Church as it stood; Joseph Smith wanted to create a new Christian Church from the ground up.
Obviously, it's not just two people - there were many who were active in the rise of Islamic fundamentalism. In his book Islamic Fundamentalism, Choueiri identifies two other major figures in addition to Qutb - Jamal ad-Din al-Afghani (1839-1897) and Abul A'la Maududi (1903-1979). He puts those three as the most important ideologues in the formation of Islamic fundamentalism, but obviously there would be others.
The reason Qutb is at the top of the list is twofold - first, because he took control of the Muslim Brotherhood in Egypt and arguably made it the largest and most radicalized Islamist movement of his era; and second, because he was a primary influence on Osama bin Laden and Ayman al-Zawahiri, the founders of al Qaeda, and spiritual forbears to ISIS. So while Qutb wasn't exclusively responsible for the rise of Islamic fundamentalism, he likely has been more influential in its ascendance than any other ideologue, and when we talk about the ideas of Islamic fundamentalism, many of those ideas are his.