According to the famous International Genearlogical Index this rare surname is recorded as Treadgar, Treadgear, Tradgar, Thredgor, Tredger, and Trudger. All seem to be quite rare. It is locational and almost certainly from Tredegar, the former mining village on the Welsh-English borders in the equally former county of Monmouthshire. Welsh surnames are almost exclusively patronymics, whilst this is locational. It is not apparently listed in the Welsh Surnames directory suggesting that nameholders when found are regarded as English! Certainly locational surnames are usually "from" names. These were names given to people as easy identification, after they left their former homes to live somewhere else. Given that over the centuries local dialects were very thick and spelling at best erratic, often as with this name, lead to the creation of "sounds like" spellings. Examples of recordings found in the surviving church registers of the city of London include John Boustead Tredger, at St Andrews Holborn, on March 8th 1767, and Mary Treadger, the daughter of Robert and Judith, who was christened at St Mathews Bethnal Green on November 17th 1805, one month after the famous battle of Trafalgar.