Who are the Houthis?

Here is an excellent documentary about the rise of the Houthis from BBC News. The narrator, Safa Al-Ahmad, is from BBC Arabic and spent three months following the Houthis and even got access to their enemies, the Sunni tribal leaders and Al-Qaeda fighters.

It runs just over 40 minutes but it explains who the Houthis are, what they want, and how they have succeeded so far.

UPDATE: You can see the full 54 minute documentary here at Frontline.. The PBS NewsHour also broadcast a portion of the documentary which you can see below.