After the jump, my goal will be to catch you up to speed on the complex character of Dr. Henry Pym...
Dr. Henry Pym is one of the most important, complicated and enduring characters in the Marvel universe. He is one of Marvel's hierarchy of genius-level intellects, on par with Bruce Banner, Tony Stark, Reed Richard, T'Challa and, of course, Peter Parker. While it's easy to say Hank Pym is Ant-Man, it would be an inaccuracy on two counts: Hank Pym was the first Ant-Man but he has also put on many other suits and taken many other name over 50 years of stories.
Deeply intertwined in the history of Hank Pym is Janet Van Dyne, his partner and eventual wife. The two were a part of the original group of heroes that assembled to slow down the rampaging Hulk who was being manipulated by Loki. Pym and Van Dyne have a long and tumultuous relationship and, at times, Van Dyne's affections go unrequited by Pym who is often wholly engrossed in his work. During his early years as an Avenger, Pym also altered his size to become Giant-Man and helped in the defeat of many Avengers foes, including the Masters of Evil.
Pym has also taken the aliases of Yellowjacket, Goliath and The Wasp during his career. While Pym has spent his career pushing the limits of technology to help humanity, his most well-known creation is the robot Ultron, the titular villain of the Avengers sequel, who has spent his entire existence trying to eliminate the entire human race. While that will reportedly NOT be a part of the MCU version of Pym, his 50 years in the comics provide plenty of other stories from which to choose.
Actor Michael Douglas was recently cast as Pym in the film. It appears that the MCU version of Pym will be a bit older than the comic counterpart and will have had his adventures fighting Communism in the 1960s before making way for Scott Lang, played by Paul Rudd, to fill the shoes of Ant-Man.
There you are...intro level Henry Pym.