http://en.wikipedia.org/wiki/Jeremy_Brett
He wanted to be the best Sherlock Holmes the world had ever seen.^[6] He conducted extensive research on the great detective and Sir Arthur Conan Doyle himself, and was very attentive to discrepancies between the scripts he had been given and Conan Doyle's original stories.^[7] One of Brett's dearest possessions on the set was his 77-page "Baker Street File" on everything from Holmes' mannerisms to his eating and drinking habits. Brett once explained that "some actors are becomers — they try to become their characters. When it works, the actor is like a sponge, squeezing himself dry to remove his own personality, then absorbing the character's like a liquid".^[8]
Brett was obsessed with bringing more passion to the role of Holmes. He introduced Holmes' rather eccentric hand gestures and short violent laughter. He would hurl himself on the ground just to look for a footprint, he would leap over furniture or jump on the parapet of a bridge with no regard for his own personal safety.
Holmes' obsessive and depressive personality fascinated and frightened Brett. In many ways Holmes' personality resembled Brett's own, with outbursts of passionate energy followed by periods of lethargy. It became difficult for Brett to let go of Holmes after work. He had always been told that the only way for an actor to stay sane was for him to leave his part behind at the end of the day, but Jeremy started dreaming about Holmes, and the dreams turned into nightmares.^[9] Brett began to refer to Sherlock Holmes as "You Know Who" or simply "HIM": "Watson describes You Know Who as a mind without a heart, which is hard to play. Hard to become. So what I have done is invent an inner life".^[10] Brett invented an imaginary life of Holmes to fill the hollowness of Holmes' "missing heart", his empty emotional life. He imagined :"...what You Know Who's nanny looked like. She was covered in starch. I don't think he saw his mother until he was about eight years old..." etc.^[10] While the other actors disappeared to the canteen for lunch, Brett would sit alone on the set reading the script, looking at every nuance,^[11] reading Holmes in the weekends and on his holidays. "Some actors fear if they play Sherlock Holmes for a very long run the character will steal their soul, leave no corner for the original inhabitant", he once said.^[12] It never occurred to him that he was ill.
... Brett struggled with filming the third Granada series, The Return of Sherlock Holmes in late 1985. On the set it was noticed that his manic episodes, his excessive changes of mood, were getting worse and eventually grief and workload became too much; he had a breakdown, was hospitalised and diagnosed manic-depressive.
Jeremy Brett was given lithium tablets to fight his manic depression. He knew that he would never be cured; he had to live with his condition, look for the signs of his disorder and then deal with it.^[18] He wanted to go back to work, to play Holmes again. The first episode to be produced after his discharge was a two-hour adaption of The Sign of the Four. From then on the difference in Brett's appearance slowly became more noticeable as the series developed. One of the side effects of the lithium tablets was fluid retention. Brett began to look and act differently. The drugs were slowing him down; he was putting on weight and retaining water.
... During the last decade of his life, Brett was treated in hospital several times for his mental illness, and his health and appearance visibly deteriorated by the time he completed the later episodes of the Sherlock Holmes series. During his later years, he discussed the illness candidly, encouraging people to recognise its symptoms and seek help.

"Holmes is the hardest part I have ever played — harder than Hamlet or Macbeth. Holmes has become the dark side of the moon for me. He is moody and solitary and underneath I am really sociable and gregarious. It has all got too dangerous".
http://www.brettish.com/jeremybrett-faq.html

http://www.deanradin.com/