Llywarch Hen (doslovno 'Llywarch Stari'; 6. vijek) bio je princ britskog (post-rimskog) kraljevstva Rheged koje je priadalo Hen Ogleddu ('Stari Sjever', današnja južna Škotska i sjeverna Engleska). Otac mu je bio kralj Cynfarch Oer, a nećak kralj Urien. Poznat je prije svega kao protagonist danas izgubljene velške srednjovjekovne pjesme u kojoj izražava žaljenje zbog smrti svog nećaka Uriena te dolazi u Rheged sa njegovom odrezanom glavom; nakon što se protiv njega okrenu rhegedski plemići, Llywarch pronalazi utočište na jugu, u Powysu.
- Ifor Williams (ed.), Canu Llywarch Hen (University of Wales Press, 1935). Original Welsh text, edited with notes.
- Ford, Patrick K. "Llywarch, Ancestor of Welsh Princes." Speculum 45.3 (1970): pp. 442–50.
- Jackson, Kenneth. "The Poems of Llywarch the Aged." Antiquity 9:35 (1935): 323-7.
- Rowland, Jenny. Early Welsh Saga Poetry: A Study and Edition of the Englynion. Cambridge, 1990.
- Sims-Williams, Patrick. "The Provenance of the Llywarch Hen Poems: A Case for Llan-gors, Brycheiniog." Cambrian Medieval Celtic Studies 26 (1993): 27-63.
- Sims-Williams, Patrick. "The Death of Urien." Cambrian Medieval Celtic Studies 32 (1996): 25-56.
- Williams, Ifor, Sir. "The poems of Llywarch Hên (Sir John Rhys Memorial Lecture)." Proceedings of the British Academy 18 (1934 for 1932): 209-302.
- Williams, Ifor, Sir. Lectures on Early Welsh Poetry. Dublin, 1944.