Complex sentence: Gilbert Whitehand (also Gilbert with the White Hand) is a member of Robin Hood's merry men about whom next to nothing is known; it is possible that he is a character known from oral literature, with only allusions remaining in written literature.
Split into simpler sentences: Gilbert Whitehand (also Gilbert with the White Hand) is a member of Robin Hood's Merry Men about whom next to nothing is known. It is possible that he is a character known from oral literature, with only allusions remaining in written literature.