Harper Lee, the author of To Kill a Mockingbird, has died at the age of 89. The book remains a towering presence in American literature, telling the tale of a white lawyer defending a black man accused of rape in the Deep South. It sold more than 40 million copies worldwide and 55 years after it was published, in 2015, she released the sequel, Go Set a Watchman. Tributes have been paid to the Alabama-born writer, who rarely gave interviews despite her fame. Former US President George W Bush, who awarded her the Presidential Medal of Freedom in 2007, said she was “a legendary novelist and lovely lady”.