Here are some examples of Welsh names starting with "T" or "D" which would be appropriate for the 13th century. The forms in parentheses are the "standard" Welsh forms; the names listed are given in the spellings we found in 13th-century records. The spellings we found have been influenced by English spelling conventions, and would be appropriate for your persona.
Tangwystl verch Morgant Glasvryn researched this letter.
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Academy of S. Gabriel