To Kill a Mockingbird author Harper Lee has died at the age of 89.

Mockingbird 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.

The book sold more than 40 million copies worldwide and 55 years after it was published, in 2015, Harper Lee released the sequel, Go Set a Watchman.

Tributes have been paid to the writer, who rarely gave interviews despite her fame.

George W. Bush, who awarded Harper Lee the Presidential Medal of Freedom in 2007, said she was “a legendary novelist and lovely lady”.

Harper Lee was born 1926 in Monroeville, Alabama. She was the youngest of four children of lawyer Amasa Coleman Lee and Frances Cunningham Finch Lee.

She was a guardedly private person, respected and protected by residents of her town, rarely giving interviews.

Harper Lee’s literary agent Andrew Nurnberg said: “Knowing Nelle these past few years has been not just an utter delight but an extraordinary privilege.

“When I saw her just six weeks ago, she was full of life, her mind and mischievous wit as sharp as ever. She was quoting Thomas More and setting me straight on Tudor history. We have lost a great writer, a great friend and a beacon of integrity.”

The manuscript for the sequel to To Kill a Mockingbird, Go Set A Watchman was discovered and published in 2015.

Many bookshops remained open all night to cope with demand on the day of the novel’s release last July.

The book is set 20 years after the events of To Kill a Mockingbird – although Harper Lee actually wrote Go Set a Watchman first.

Watchman contains some of the same characters as Mockingbird, including Scout and her father Atticus Finch.

The publication proved controversial as early reviewers noted that Atticus Finch expresses racist views in the story.

In 1962, To Kill a Mockingbird was made into a film starring Gregory Peck as Atticus Finch and Mary Badham as Scout. The novel is currently being adapted for the stage.