Ian Holm's tightly-wound nerviness has been the secret of his success for 50 years
As many theatrical knights have discovered, taking a key part in a blockbuster movie can be a double-edged sword: you're revered by millions of kids, but the role eclipses all the classy, grown-up stage and screen work you've sweated over for years. When Sir Ian Holm took the part of Bilbo Baggins in Peter Jackson's Lord of the Rings trilogy in 2001, and then reprised it for The Hobbit trilogy, did he wonder if all h…