David Cameron's great-great-great-great-great-granddad

As Britannia.com tells it:

William succeeded his brother, George IV, and was welcomed with open arms by the British public, who had grown weary of the excesses of the fourth George. William possessed an unassuming character, exemplary private life and disdain for pomp and ceremony. Court life became somewhat lackluster, adding to the generally low opinion that had formed concerning the monarchy. William did little to counteract such feelings, but never generated the embarrassment and scandal of his Hanoverian predecessors.

Information on Cameron's descent from the Sailor King here.