The Twelve Peers of Charlemagne are twelve knights that serve the King of the Frankish Realm, Charlemagne. As a cousin of Roland, Astolfo is included among those twelve-- that being said, Astolfo was famed as ｢weak｣ in legends.
Unprecedented, of immature skill, thoughtless, et cetera. In any case, Astolfo remained unaffected by such hearsay and, as a knight, guided all sorts of difficulties to their resolutions. Incidentally, Astolfo's attire is something meant to appease Roland, who once ran wild due to a broken heart.

He's one of the most famous traps (a boy who looks like a girl, vice versa) in Fate series. Because of that, there are lots of his fanart drawn looking like a full-fledged girl and hard to search for his badass, more manly artwork.

So I made one :p