TV's most-watched history series brings to life the compelling stories from our past that inform our understanding of the world today.

An officer for a security agency that regulates time travel, must fend for his life against a shady politician who has a tie to his past.

In 1964, a brash, new pro boxer, fresh from his Olympic gold medal victory, explodes onto the scene: Cassius Clay. Bold and outspoken, he cuts an entirely new image for African Americans in sport with his proud public self-confidence and his unapologetic belief that he is the greatest boxer of all time. Yet at the top of his game, both Ali's personal and professional lives face the ultimate test.