Question: Which character's past is explored in J.K. Rowling's sixth Harry Potter novel?
Context: Magic Beyond Words: The J.K. Rowling Story is a made-for-TV film starring actress Poppy Montgomery.  It is based on the book "J.K. Rowling A Biography", by Sean Smith, detailing the journey of struggling single mother J. K. Rowling, her bid to become a published author, and her rise to fame that followed the publication of "Harry Potter and the Philosopher's Stone". Pottermore is the digital publishing, e-commerce, entertainment and news company from J.K. Rowling and is a global digital publisher of Harry Potter and J. K. Rowling's Wizarding World.  It offers news, features, and articles as well as new and previously unreleased writing by J.K. Rowling.  The site features Rowling's thoughts, several pages of unpublished text, and a sales resource for e-book and audiobook versions of the seven "Harry Potter" novels. Sam Clemmett is a British actor.  Born in Brundall, Norfolk, Clemmett began his acting career in 2013.  He is known for being cast as Albus Potter in 2015 for the British play Harry Potter and the Cursed Child.  His performance in the play has made him popular with Harry Potter fans, as well as the creator of Harry Potter, J.K. Rowling.  Rowling stated that, "There's much I could say about Sam-as-Albus, but we'd be into spoiler territory so quickly I'll just say we couldn't have cast better."  He played the role in the West End, until late-Spring 2017. Half-Blood Prince generally refers to the novel "Harry Potter and the Half-Blood Prince" by J. K. Rowling. The Magical Worlds of Harry Potter: A Treasury of Myths, Legends, and Fascinating Facts is a guide to the fictional "Harry Potter" universe, written by David Colbert.  It explores the references to history, legends, and literature in J.K. Rowling's "Harry Potter" novels.  Colbert conceived the idea for "The Magical Worlds of Harry Potter" while quizzing his nephew and nieces about the mythological references in the novels.  He later wrote the book while teaching a seminar on self-publishing to graduate students at the University of North Carolina.  The book was published in March 2001, without approval from Rowling, and has since received positive reviews from critics.  An updated version of "The Magical Worlds of Harry Potter" was published in 2004 by Berkley Books. Melissa Anelli (born December 27, 1979) is an American author and webmistress.  She is the author of the "New York Times" bestseller "Harry, A History", which chronicles the "Harry Potter" phenomenon with exclusive interview material and a foreword written by "Harry Potter" creator J.K. Rowling.  Anelli is also the full-time webmistress of The Leaky Cauldron, a commercial fansite devoted to the "Harry Potter " franchise for fans. The "Harry Potter" series of fantasy novels by J. K. Rowling have become some of the most widely read works of children's literature in history, with readers of all ages and in many countries.  In April 2011 worldwide sales of Harry Potter books were estimated to be about 450 million copies.  Oddly enough, it has been difficult to accurately determine with any degree of certainty exactly how many languages Harry Potter has been translated into.  As best as can be determined (as of 2017), The Philosopher's Stone has been officially translated from the original English into 73 other languages.  A 74th language, Scots, was announced on 2017-06-28 and it is expected to be available in October, 2017.  Both Bloomsbury's and J.K. Rowling's sites have recently stated that the books have been translated into 79 languages (80 with the 2017-06-28 announcement of Scots); however, it has been argued that number actually represents the number of authorized translations (of The Philosopher's Stone) plus the original English.  The number of authorized translations is not equal to the number of languages because there have been multiple authorized translations into the same language.  Specifically, there have been two separate translations into each of: Mandarin Chinese, Portuguese, Romanian, Russian and Turkish (5 languages).  English is often included in the list of translations even though technically it should not be (indeed, it is why our list here counts up to 74).  Thus: 79 − English − 5 double-translations = 73.  It is also worthwhile to emphasize that not all seven books are have been translated into these 73 languages. Harry, A History: The True Story of a Boy Wizard, His Fans, and Life Inside the Harry Potter Phenomenon is a 2008 book by writer and webmistress of The Leaky Cauldron, Melissa Anelli.  The book describes the "Harry Potter" phenomenon in detail.  The book was published on November 4, 2008, by Pocket Books, and debuted at #18 on "The New York Times" paperback bestseller list.  Notably, the book features exclusive interview material and insights from Harry Potter author J.K. Rowling who also wrote the foreword. The James Potter series is an unofficial sequel-series of J.K. Rowling's Harry Potter universe, written by G. Norman Lippert.  The novel series centers around the character of James Sirius Potter, Harry Potter's son, a character who makes a fleeting appearance in the novel "Harry Potter and the Deathly Hallows".  The series starts with his first year at Hogwarts, set one year before the end of the Harry Potter series. Harry Potter and the Half-Blood Prince is the sixth and penultimate novel in the "Harry Potter" series, written by British author J. K. Rowling.  Set during protagonist Harry Potter's sixth year at Hogwarts, the novel explores the past of Harry's nemesis, Lord Voldemort, and Harry's preparations for the final battle against Voldemort alongside his headmaster and mentor Albus Dumbledore.
Answer: Lord Voldemort