Question: Which former roommate of Mark Zuckerberg owns 53 million Facebook shares? 

Context articles: Facebook Graph Search
The Social Network
History of Facebook
The Accidental Billionaires
Chan Zuckerberg Initiative
Randi Zuckerberg
Eduardo Saverin
Mark Zuckerberg book club
Facebook Beacon
Priscilla Chan (philanthropist)

Facebook Graph Search was a semantic search engine that was introduced by Facebook in March 2013.
 It was designed to give answers to user natural language queries rather than a list of links.
 The Graph Search feature combined the big data acquired from its over one billion users and external data into a search engine providing user-specific search results.
 In a presentation headed by Facebook CEO Mark Zuckerberg, it was announced that the Graph Search algorithm finds information from within a user's network of friends.
 Additional results were provided by Microsoft's Bing search engine.
 In July it was made available to all users using the U.S. English version of Facebook.
 In December 2014, Facebook changed its search features, dropping partnership with Bing, and eliminating most of the search patterns.
The Social Network is a 2010 American biographical drama film directed by David Fincher and written by Aaron Sorkin.
 Adapted from Ben Mezrich's 2009 book "The Accidental Billionaires: The Founding of Facebook, A Tale of Sex, Money, Genius, and Betrayal", the film portrays the founding of social networking website Facebook and the resulting lawsuits.
 It stars Jesse Eisenberg as founder Mark Zuckerberg, along with Andrew Garfield as Eduardo Saverin, Justin Timberlake as Sean Parker, and Armie Hammer as Cameron and Tyler Winklevoss.
 Neither Zuckerberg nor any other Facebook staff were involved with the project, although Saverin was a consultant for Mezrich's book.
 The film was released in the United States by Columbia Pictures on October 1, 2010.
Facebook is a social networking service launched on February 4, 2004.
 It was founded by Mark Zuckerberg with his college roommate and fellow Harvard University student Eduardo Saverin.
 The website's membership was initially limited by the founders to Harvard students, but was expanded to other colleges in the Boston area, the Ivy League, and gradually most universities in the United States and Canada, corporations, and by September 2006, to everyone with a valid email address along with an age requirement of being 13 and older.
The Accidental Billionaires: The Founding of Facebook, A Tale of Sex, Money, Genius, and Betrayal is a 2009 book by Ben Mezrich about the founding of Facebook, adapted by Columbia Pictures for the 2010 film "The Social Network".
 Co-founder Eduardo Saverin served as Mezrich's main consultant, although Mark Zuckerberg declined to speak with him while the book was being researched.
 After Zuckerberg and Saverin settled their lawsuit, Saverin broke off contact with the author.
The Chan Zuckerberg Initiative (CZI) is a limited liability company founded by Facebook founder Mark Zuckerberg and Priscilla Chan with an investment of "up to $1 billion in [Facebook] shares in each of the next three years".
 Its creation was announced on December 1, 2015, for the birth of their daughter, Maxima Chan Zuckerberg.
Randi Jayne Zuckerberg (born February 28, 1982) is an American businesswoman.
 She is the former Director of Market Development and spokesperson for Facebook, and a sister of the company's co-founder and CEO Mark Zuckerberg.
 Prior to working at Facebook, she was a panelist on "Forbes on Fox".
 As of May 2014, she is founder and CEO of Zuckerberg Media, editor-in-chief (EIC) of Dot Complicated, a digital lifestyle website, and creator of Dot., an animated television show about a young girl (the eponymous Dot) who uses technology to enhance both her educational experiences and recreational activities, which airs on Sprout.
Eduardo Luiz Saverin ( ; ] ; born March 19, 1982) is a Brazilian Internet entrepreneur and angel investor.
 Saverin is one of the co-founders of Facebook.
 s of 2015 , he owns 53 million Facebook shares (approximately 0.4% of all outstanding shares) and has a net worth of $8.7 billion, according to "Forbes".
 He has also invested in early-stage startups such as Qwiki and Jumio.
Mark Zuckerberg book club aka A Year of Books was an online book club hosted by Mark Zuckerberg through his personal Facebook account started in January 2015.
 Zuckerberg made a book recommendation every two weeks for a year to his millions of Facebook followers.
Beacon formed part of Facebook's advertisement system that sent data from external websites to Facebook, for the purpose of allowing targeted advertisements and allowing users to share their activities with their friends.
 Beacon would report to Facebook on its members' activities on third-party sites that also participate with Beacon.
 These activities would be published to users' News Feed.
 This would occur even when users were not connected to Facebook and would happen without the knowledge of the Facebook user.
 One of the main concerns was that Beacon did not give the user the option to block the information from being sent to Facebook.
 Beacon was launched on November 6, 2007 with 44 partner websites.
 The controversial service, which became the target of a class-action lawsuit, was shut down in September 2009.
 Mark Zuckerberg, CEO of Facebook, characterized Beacon on the Facebook Blog in November 2011 as a "mistake".
 Although Beacon was unsuccessful, it did pave the way for Facebook Connect, which has become widely popular.
Priscilla Chan (born February 24, 1985) is an American pediatrician and philanthropist.
 She is the wife of the co-founder and CEO of Facebook, Mark Zuckerberg.
 Born and raised in Massachusetts, she attended Harvard University for undergrad and received her medical degree from the University of California, San Francisco (UCSF).
 As of 2015, she and her husband have pledged more than $1.6 billion to charities.
 In December 2015, they pledged to donate 99% of their Facebook shares, valued at $45 billion, to the Chan Zuckerberg Initiative, a philanthropic and political action company that focuses on health and education.