The portrait of William Herbert, Earl of Pembroke (c.1501-1570).

The image is in the public domain because it is a copy of a work whose original creator died several centuries ago.

Burke, Sir Bernard. [Burke's general armory] : The General armory of England, Scotland, Ireland and Wales. London : Harrison, 1884. [Available online at the Internet Archive]
Dictionary of Welsh biography [website] : Cradock, Sir Matthew or Mathias.
Fairbairn's book of crests of the families of Great Britain and Ireland. Volume 1. Fourth edition. London : T.C. & E.C. Jack, 1905.
Hughes, Anthony, and the Swansea U3A iPad team. Discovering your Guildhall. 2nd edition, 2020.
Morgan, Ernest. Heraldic shields in grand corridor, Guildhall, Swansea. 1936
Wikipedia [website] : William Herbert, 1st Earl of Pembroke (died 1570).

Acknowledgements (Sir Matthew Cradock)