Llywelyn Siôn

Llywelyn Siôn (1540 – c.1615) was a Welsh language poet.

Although remembered as a poet, he was also a professional manuscript copyist. Iolo Morganwg claimed he was the author of Cyfrinach Beirdd Ynys Prydain, used by the Welsh Gorsedd, but it is now known that Iolo himself was the author of that work. Additionally, the work known as Barddas was attributed to him when it was published, but was later revealed to have been based on manuscripts forged by Morganwg.