So you're not a comics lover, but you loved The Avengers. So much that, knowing that Marvel hid teaser scenes at the end of all their other films, they probably hid one at the end of The Avengers. You stayed, and you got so excited you gave yourself a glute massage on the theater-seat with your excited butt-wiggling, and then it CAME ON! And you're back in space, and there's Creepy Two-Thumbs guy, and he's talking to somebody, and the somebody turns around, and the one thought on your mind is—who is that purple guy?
Don't worry! You weren't the only one that was slightly confused. Sure, he promises a villain for Avengers sequels, but his big purple face means nothing to you. Whereas your Marvel-loving nerd-friend next to you started having an asthma attack, grabbed you, and said "Isn't that awesome!? Oh my Galactus!"
"Who?" you reply.
"That's Thanos! The Mad Titan!"
So here's what you need to know about this guy:
1. He's an alien sort-of-god. He's from Saturn's moon Titan, is an Eternal, and is pretty much immortal.
2. He's in love with Death. The entity and the actual thing. He killed just about everyone else on his planet simply because he wanted to impress Death (Death's a girl. Guys do crazy things for girls.)
3. If he gets the Tesseract (that shiny white cube all the fuss in Captain America and The Avengers was about), he'll probably become all-powerful. So the Avengers better watch out.
He will almost definitely be the villain for the next film, so now, you know what his dealio is and you don't have to be confused! You're welcome.