The large SUV brand is based on the Humvee military vehicle. It was always a niche vehicle but its image and sales were hit particularly hard by rising gasoline prices earlier this decade. Lately, they have been able to sell only a few Hummer units so that made its situation worse.
Hummer is the third brand that GM is being forced to shut down as part of its bankruptcy reorganization last year. A deal to sell Saturn fell through and GM is also closing the Pontiac brand, which it never attempted to sell.
I was lucky enough to get inside a Hummer vehicle in 2007 when I was in Disney MGM theme park and have a photo taken. Too bad though that GM is bidding farewell to this brand.