Transferred use of the Scottish surname. The principal family bearing this surname were hereditary Earls Marischal of Scotland from 1455 to 1715. This is one of a number of Scottish aristocratic surnames that have become well established since the 19th century as boys' names throughout the English-speaking world, not just in Scotland. Others include Bruce, Douglas, and Graham.
English: patronymic from Weather, from Middle English wether ‘wether’, ‘(castrated) ram’ (Old English weðer), hence a nickname for a man supposedly resembling a wether, or a metonymic occupational name for a shepherd.