Cafodd pob un o’r bedair cyfres, gyda chymorth Llywodraeth Cymru, a chyfnogaeth Sgrîn Cymru, eu ffilmio a’u cynhyrchu yng Nghymru, ac mae’r gyfres wedi ei lleoli yng Nghaerdydd a’r ardal.  Roedd y gyfres yn apelio’n fawr at gynulleidfaoedd ym Mhrydain a thramor a’r drydedd gyfres oedd y gyfres ddrama fwyaf poblogaidd ym Mhrydain ers 2001.
All four series, backed by the Welsh Government and assisted by Wales Screen, were filmed and produced in Wales and based in and around Cardiff. The award winning show has proved to have massive appeal for audiences in the UK and overseas and the third series was the UK's most watched drama series since 2001.