|“||Doesn't take much - hardly a push. Oh, America - all-you-can-eat, all the time. Consume, consume. A swarm of locusts in stretch pants. And yet, you're all still starving because hunger doesn't just come from the body, it also comes from the soul.
~ Famine, speaking to Dean
Famine is one of the Four Horsemen of the Apocalypse, the physical manefestation of hunger and starvation. Famine used to be very powerful in the past, but because of progress like farming and agricultural genetically modified crops and other advances, Famine was less powerful than he used to be (hence his crippled, immobile state throughout the season). However, this did not deter Famine from actively joining in the Apocalypse - Castiel said that once Famine got his strength back, he would "march across the lands" with authority.
He appeared in the episode "My Bloody Valentine" and he was infecting people with his hunger causing them to live their hungers, such as food, drink, sex etc. until it killed them. Famine got stronger by devouring souls, which is why he was causing chaos, to regenerate. Famine carried a black briefcase, like his brother Death, and he collected the souls of the people he consumed in the case.
He was defeated when Sam exorcised Famine's group of demon servants, and Famine devoured them out of hunger. However Sam was able to exorcised the demons from within Famine. This weakened Famine to the point that Sam and Dean were able to take his ring defeating him, and preventing him from being able to maintane physical form.
It seems later on in the season that Famine and War are not active anymore since they lost their rings and they both became immobile, powerless husks, unable to move unless, possibly, one gave them their rings back.