Artist Charlie Wren shared the concept art for Mjolnir, Thor's mighty hammer, as it was developed for the Marvel Cinematic Universe. Oh, these weren't the only ideas, but they are the many that were approved by Marvel as the process went along. Any of them would have been fine by me, but after three Thor movies and four Avengers movies, it would be hard to accept anything but the final Mjolnir. Click on the pictures to see them in full. -via io9