He is one of the Knights of the Round Table.

Galahad was a later addition to the Round Table, especially famed for his escapades in the search for the Holy Grail. Galahad is the son of Lancelot, but he only saw Lancelot as a father while he was a boy and both never got along that well. Galahad was admired as the perfect knight, the young boy who would shoulder the next generation of the Round Table. He was a "saint who was the only one to obtain the Holy Grail, just to return it to heavens."

Lancelot comments that Mash Kyrielight is wearing her hair in a similar style to him.

As Mash goes through her second to last Saint Graph Ascension, Bedivere describes her appearance is completely like Galahad.

(Source: Wiki)