As soon it was announced that Harper Lee passed away early Friday, social media was filled with tributes to the 89-year-old author.

Perhaps most remarkable is that Lee made such an impact despite having published only two novels, one of which wasn’t even out until 2015. It was her 1960 novel To Kill a Mockingbird that made her career, becoming an instant bestseller, a blockbuster film and wracking up numerous awards in the process. To Kill a Mockingbird has sold over 40 million copies worldwide and has been translated into 40 languages.

What many do not know, however, is that a very generous Christmas gift from her friends made it possible for her to write the novel that has now become part of almost every American high school’s curriculum. In 1956, a few of Lee’s friends pooled money together so they could give their friend a year off from work. The note accompanying the money read “You have one year off from your job to write whatever you please. Merry Christmas”.

After Lee wrote Go Set a Watchman, which wouldn’t end up being published until 2015, an editor convinced her to write a novel from the childhood perspective of the protagonist Scout. In 1960, that novel, To Kill a Mockingbird, was published. A bestseller, it was made into a movie two years later. The film won an Academy Award for Best Actor. The novel earned Lee a Pulitzer prize in 1961. She was 35 at the time. In a 1964 interview with New York radio station WQXR, Lee said “all I want to be is the Jane Austen of South Alabama.”

Gregory Peck as Atticus Finch, Mary Badham as Jean Louise 'Scout' Finch and Phillip Alford as Jeremy 'Jem' Finch in To Kill a Mockingbird Gregory Peck as Atticus Finch, Mary Badham as Jean Louise ‘Scout’ Finch and Phillip Alford as Jeremy ‘Jem’ Finch in “To Kill a Mockingbird”Photograph by Silver Screen Collection/Getty Images

After the novel was published, Lee retreated out of the spotlight for basically the rest of her life, preferring to live outside the public’s eye. Her book, however, continued to earn her money year after year.

According to a 2013 court case filed against Lee’s former agent Sam Pinkus, she earned $2.5 million in royalties from To Kill A Mockingbird between July 2009 and July 2010. Assuming that time frame represents an average gross from the book, Lee earned over $9,000 per day off of the novel.

Even more than 50 years after it was first published, the novel still sells 750,000 copies a year.

In 2007, Lee was honored by President George W. Bush with the Presidential Medal of Freedom for her contribution to literature. In 2010, President Obama awarded her the National Medal of Arts.

Author Harper Lee receiving the Presidential Medal of Freedom in 2007Chip Somodevilla—Getty Images

In July 2015, at age 88, Lee released her second novel, Go Set a Watchman. It made history by being the fastest-selling book in the 26-year history of HarperCollins Publishers. Barnes and Noble also said that first-day sales of the book outpaced all other adult fiction books in the company’s history, toppling a record that had been held since 2009 by Dan Brown’s The Lost Symbol. Amazon also said the novel was the most pre-ordered print title since the 2007 release of Harry Potter and the Deathly Hallows.

The release of the novel, while incredibly successful, was also shrouded in controversy. Many questioned Lee’s health—she had a stroke a few years earlier and was very poor of sight and hearing. In a 2011 letter, Lee’s sister wrote, “Poor Nelle Harper can’t see and can’t hear and will sign anything put before her.” Many wondered whether Lee was in the right state of mind to sign documents and whether or not she actually wanted the book released.

Just this year, more Lee news was released. To Kill a Mockingbird is set to be turned into a Broadway play for the 2016-2017 season. The play will be written by Aaron Sorkin, who also wrote The Social Network and Steve Jobs.

Since Lee never married or had children, and her closest relative was her sister Alice who passed away in 2014, many are left wondering what will happen to Lee’s estate. It’s only a matter of time before that question is answered.

Without a doubt, Lee’s legacy will live on for many years to come.