Becket, starring Richard Burton as Thomas Becket and Peter O'Toole as king Henry II. It showed on Cinemax, and I had a VHS copy of it that I watched so many times I had memorized the film by the time I went to college.
Based on a 1959 play by Jean Anouilh, the film chronicles first the close friendship, and eventual hateful ending, between Thomas Becket and the English king Henry II. Becket is seen as sharing in many of the king's lusty adventures, ever the watchful friend and accomplice, the film very effectively sets up the two as being inseparable, with Becket being the only close friend Henry actually has. Becket is made Chancellor of England, to the consternation of the Norman nobility (Becket being a Saxon, and no love being lost between the two English races). The close friendship is also resented by the Queen (who unfortunately is given a completely forgettable part in this film, considering she is Eleanor of Aquitaine, one of the most notable figures in all of Medieval history). Becket is not only envied for his friendship with the king, but also for his fierce intellect and political acumen. The king calls him "the only intelligent man in England" at one point, and Becket's talents are used to blunt the aspirations of the Church to exercise independence from the king's laws.
When the Archbishop of Canterbury dies, Henry hits on the notion of appointing Becket as his successor, thus making "Canterbury for the king." Becket protests, but the king insists, and the stage is set for their break. For, as he ascends to the Archbishopric, Becket decides that his honor requires that he actually fulfill the office to the best of his abilities. Where he once took the side of the crown in the struggle between king and Church, he now finds himself on the other side of the fight. And it is a betrayal that Henry can never forgive.
The struggles between Becket and Henry become more and more tense until Becket is forced to flee to France, eventually traveling to Rome to seek the Pope's support. There is a nice scene between Becket and Louis, king of France (played by John Gielgud), following a complete snubbing of Henry's ambassadors by the French king. Eventually, Becket is placed into exile at a monastery, and then returns to England after a compromise is reached between the two former friends. But it is the anguish on Henry's face, when he realizes things will never be as they were, and where the trajectory of events will inevitably lead, that makes the politicking great cinema. It's not just empty posturing about the enforcement of obscure laws. It's about the final destruction of a friendship, and eventually, the friend himself.
The film ends with, of course, the death of Becket following the most famously ambiguous royal command in history; "Will no one rid me of this meddlesome priest?"
What really makes this film is the acting. Richard Burton is, well, Richard Burton, and you can never get a bad performance out of him. But Peter O'Toole is beyond his usual brilliant self as Henry, at home bellowing orders at the top of his lungs, and equally so selling the king as a lovable rascal and rogue. O'Toole reprised the role for 1968's The Lion in Winter, which is in and of itself a terrific film, where it is great to see Henry back to bellowing and shouting at his family and everyone else around him. (And, I should point out, the magnificent Katherine Hepburn does a virtuoso performance as the aforementioned Eleanore of Aquitaine.)