I just saw a great film about "The Greatest," another person of Irish descent, titled The Trials of Muhammad Ali. The documentary doesn't delve into Ali's Irish roots. It focuses mainly on his conversion to Islam and his resistance to the draft during the Vietnam War. It's a fascinating story, and the film is very well-made. You can find upcoming screenings for the film on the website. It's getting theatrical release, which comes as no surprise because the film is so good.
Here's a very entertaining interview -- Cathal O'Shannon's 1972 interview with Ali on RTE.
Then there's this video about Ali's 2009 visit to Ennis. It explains Ali's Irish lineage going back to his great-grandfather who was born in Ennis and includes an interview with one of his cousins.