In recent times I've read two similarly titled biographies of George. Elliot J Huntley's Behind that Locked Door and Graeme Thomson's Behind the Locked Door.
The Huntley book commences with the break-up of the Beatles and takes us til Georges death in 2001. It's a pretty slight effort. Huntley is too clearly a fan of George which skews the book too far toward his mostly favourable opinion on George's music and other activities, and less on presenting a biography of facts and analysis to help the reader make up their own mind. He always tends to give the George-friendly spin on any issue with two sides. Huntley also has an annoying habit of overdoing exclamation marks which contributes to a feeling of gosh golly fandom. That said he is not uncritical and has a nice dry sense of humour. (On the Clapton/Pattie episode he concludes by saying of Eric and Pattie 'The couple then lived happily ever after until their divorce a few years later.') It looks like Huntley wrote the book from existing resources rather than interviewing people who knew George (there's no list of interviewees or even bibliography in my kindle edition). While not a must read it's an easy read and enjoyable enough for George fans.
Thomson's book, though only around the same length as Huntley's, is much more substantial and probably the best bio of George to date. Dealing with all of George's life, it's very much warts and all. Episodes illustrating George's churlish and bitter side balance the praiseworthy aspects of his life. Thomson uses a neat device of a short pre-chapter anecdote, titled Be Here Now, to relate some incident that deals with the themes of the subsequent chapter.
He is much more objective than Huntley on George's music. On his solo career he comes across as analytical and balanced; without being reflexively dismissive of material even on George's weaker albums. (Well, perhaps Gone Troppo stretches the friendship there a bit.) His afterword where he assesses George's career and overall talents was well-argued, compelling and fair.
He suggests that, through lack of confidence and shyness, George didn't necessarily present all his strengths as a musician. George's demos and unreleased songs showed that stripped back and more intimate arrangements often suited him. Fans of George's acoustic version of While My Guitar will understand what he means.
Thomson clearly had good access to George's friends and associates so there are lots of facts and episodes in the book that are new to me. He tells a cute story of George using his celebrity to get into a Prince concert. Clearly, despite the drawbacks George was all to willing to complain about, being an ex-Beatle had perks worth using.
Thomson conveys very well the hair-tearing frustration George felt in the Beatles when his attempts to contribute more were rebuffed, just after returning from being treated as an equal by US musicians such as the Band and Bob Dylan. A quote from Glyn Johns is one of the best illustrations of the tortured relationships in the Beatles at the time and the effect particularly on George. Johns said, after George had demoed Something to him he couldn't on earth understand what was going on in the Beatles when George seemed reluctant to introduce such a song to John and Paul.
I think the Thomson book is a must read for George fans. And recommended for anyone interested in the Beatles. I wouldn't call it definitive. The authors lack of access to the remaining Beatles and Olivia and Dhani probably prevents it gaining that honour. He clearly draws a lot on Pattie Boyd's input but, as presented, it doesn't appear that she was overly negative or using it to settle scores, although her quotes often have a sad undertone. As if you can hear a wistful sigh as she delivers it.
As someone who probably listens to George's solo stuff more so than that of the other Beatles, it's good to see a bio that shows his strengths and weaknesses, rather than gushing fandom on one hand or hatchet job on the other.