It started out as the National Schizophrenia Fellowship, founded by John Pringle, who's son suffered from Schizophrenia. Back in 1970, Pringle wrote a letter to The Times about his experiences with his son, which is now on their website, it's well worth taking a few minutes to read it if you're interested.
Nowadays, they do a lot of great work, but they still aren't as widely recognised as they should be. They have an extensive website full of expert, but accessible information. I've noticed that often, the term 'mental illness' is thrown around but only to cover the more well-known issues like Depression and Anxiety. Even then, it doesn't cover the full spectrum of those.
Rethink run a range of services, including support groups, crisis housing, help with employment and training, and help that is tailored specifically towards young people. They really help to educate people about their rights, and advocate for people to get what they should have when they are unable to themselves. Both alone and by teaming up with other charities, they run campaigns that educate and raise awareness. The website is colourful and easy to navigate, I've spent a lot of time on it, (if you've never visited their site before, make sure you have plenty of time because you'll have ten tabs open in no time).
Along with giving 10% of the profits from These Endless Days to Rethink, I'll be doing my second event to raise money for them this year too, a ten-mile walk in June.