Who served as a translator and calming presence" on the Lewis and Clark Corps of Discovery expedition in 1805-06?

in afghanistan, yelda, the first month of jadi is the longest night of the year. amir says that yelda was the starless night tormented lovers kept vigil enduring the endless dark, waiting for the sun to raise and bring with it their loved. amir says he became a yelda when he met soraya in america.