Charlemaigne's grandfather who really is the start of the Karling's rise to the imperial dominance of Charlemaigne but He's known as the savior of Europe/defender of Christianity for his defeat of a Muslim army at Tours, which marked the highpoint of Islamic incursions into Western Europe.

His reputation has taken a hit semi recently as some question the actual size of the invading army (though the Chronicle of 754 claimed the muslims were outnumbered that's not the general view passed on to later generations) and/or their goal: a raid instead of an invasion.

compare that to say Gibbon's portrayal in decline and fall:

he victorious Saracen overran the provinces of Aquitain, whose Gallic names are disguised, rather than lost, in the modern appellations of Perigord, Saintonge, and Poitou: his standards were planted on the walls, or at least before the gates, of Tours and of Sens; and his detachments overspread the kingdom of Burgundy as far as the well-known cities of Lyons and Besancon. The memory of these devastations (for Abderame did not spare the country or the people) was long preserved by tradition; and the invasion of France by the Moors or Mahometans affords the groundwork of those fables, which have been so wildly disfigured in the romances of chivalry, and so elegantly adorned by the Italian muse. In the decline of society and art, the deserted cities could supply a slender booty to the Saracens; their richest spoil was found in the churches and monasteries, which they stripped of their ornaments and delivered to the flames: and the tutelar saints, both Hilary of Poitiers and Martin of Tours, forgot their miraculous powers in the defence of their own sepulchres. (29) A victorious line of march had been prolonged above a thousand miles from the rock of Gibraltar to the banks of the Loire; the repetition of an equal space would have carried the Saracens to the confines of Poland and the Highlands of Scotland; the Rhine is not more impassable than the Nile or Euphrates, and the Arabian fleet might have sailed without a naval combat into the mouth of the Thames. Perhaps the interpretation of the Koran would now be taught in the schools of Oxford, and her pulpits might demonstrate to a circumcised people the sanctity and truth of the revelation of Mahomet. From such calamities was Christendom delivered by the genius and fortune of one man [Gibbon's semi famous quote on the subject]. Charles, the illegitimate son of the elder Pepin, was content with the titles of mayor or duke of the Franks; but he deserved to become the father of a line of kings

Just to note, Martel is french for Hammer, so saying Charles Martel Hammer is redundant.