Who are Yemen's Houthis and why are they attacking Red Sea ships?

[Collection]The Iran-aligned Houthis of Yemen are playing an escalating role in the Middle East conflict, attacking shipping in the Red Sea and firing Houthi missiles and drones at Israel to support Palestinians. US defense secretary Lloyd Austin announced a multinational operation to safeguard commerce in the Red Sea in response to the Houthi attacks. The Houthis' actions threaten sea lanes for oil shipments and worry states on the Red Sea. The Houthis have a history of guerrilla wars and gained power during the Yemen war. They have an arsenal of ballistic missiles, armed drones, and naval missiles.