Final answer:
W.B. Yeats helped establish the Irish National Theater, also known as the Abbey Theatre.
Step-by-step explanation:
The Irish National Theatre was established by W.B. Yeats. Yeats, who was a well-known poet, playwright, and Nobel Laureate, played a crucial role in the establishment of the Abbey Theatre in Dublin, Ireland, which became the national theater of Ireland. He co-founded the theater with Lady Gregory and Edward Martyn in 1904, and it went on to become a significant platform for promoting Irish culture and literature.