On January 8, 1968, The Undersea World of Jacques Cousteau debuted on ABC. The show is vintage Cousteau, featuring the French adventurer-slash-scientist wearing a red cap, a skimpy bathing suit, and smoking like a chimney. In the first episode, Captain Cousteau introduced his crew, his research vessel Calypso, and proceeded to swim with sharks.
It's easy to see the clear line drawn between this documentary and modern nature films. Cousteau mixed exploration with explanation, keeping audiences informed and excited at the same time. The technical aspect is impressive as well, with color filming on the ship and underwater.
If you've seen The Life Aquatic with Steve Zissou and you haven't seen the Cousteau films, you're in for a treat.