House Mormont is an old house of The North, though not an ancient house like The Starks. However, as of the events of ASoIaF, The Mormonts are one of the principal families that are sworn to House Stark. Perhaps even more so with events that have transpired during ASoIaF if we base our assumptions on the yet-to-be-published-yet-already-adapted-material that takes place during HBO's Game of Thrones.
Tho asketh for episodes that be-eth new and giveth upon tho feelings of great excite? Tho haveth best take care of what thine asketh for! Take heed of thy warning before tho listeneth to Prophesies, Dreams, and Visions- a series of words spoken by The Promised Princes that shall long take a virtuous look at the prophetic instances tho hath found in A Song of Ice and Fire.