What is the "Patriotic Millionaires" movement?

An international movement has formed, fronted by Gary Stevenson and actor Brian Cox

Last week you may have spotted a bus out and about (or the photos of it on social media), calling for a wealth tax:

Labour MP Richard Burgon was one of the famous faces promoting it:

This bus belongs to Patriotic Millionaires UK, the British wing of the Patriotic Millionaires movement, which began in the US - spearheaded by Abigail Disney (the Disney heiress):

Although the group may seem fairly recent, The Patriotic Millionaires movement “started in 2010 with only a handful of signatures on a 163-word open letter, including the musician Moby and Ben & Jerry’s ice-cream co-founder Ben Cohen.”