Question: Richmond Park has been represented by Zac Goldsmith, who lost to who in the 2016 London mayoral election?
Context: Frank Zacharias Robin "Zac" Goldsmith (born 20 January 1975) is a British politician and journalist.  He serves as the Member of Parliament for Richmond Park having been re-elected as an MP at the snap 2017 general election, after previously holding the seat between 2010-16.  He was the Conservative Party candidate at the 2016 London mayoral election, which he lost to Sadiq Khan of the Labour Party.  Ideologically characterised as having liberal and libertarian views, he is known for his environmentalist and localist beliefs. The 2016 London mayoral election was held on 5 May 2016 to elect the Mayor of London, on the same day as the London Assembly election.  It was the fifth election to the position of Mayor, which was created in 2000 after a referendum in London.  The election used a supplementary vote system. The London Assembly election of 2012 was an election of members to the London Assembly which took place on Thursday, 3 May 2012, the same day as the London mayoral election, 2012, and the United Kingdom local elections, 2012.  Although Conservative candidate Boris Johnson won the Mayoral election, the Assembly election produced the Labour Party's best result since the inception of the London Assembly; this was subsequently surpassed by the party's performance in the 2016 election. The Richmond Park by-election was a UK parliamentary by-election in the constituency of Richmond Park which was held on 1 December 2016.  It was triggered by the resignation of the Conservative Member of Parliament Zac Goldsmith on 25 October 2016 over the Government's proposal for a third runway at the nearby Heathrow Airport.  It was won by Sarah Olney of the Liberal Democrats, after a campaign focused on opposition to Brexit. Susan Veronica Kramer, Baroness Kramer, PC ("née" Richards; born 21 July 1950) is a British Liberal Democrat politician.  She was Member of Parliament (MP) for Richmond Park from 2005 to 2010, prior to that having a career in infrastructure finance and in 2000 having been a candidate in the London mayoral election. The London mayoral election for the office of Mayor of London takes place every four years.  The first election was in held May 2000, and four subsequent elections have taken place.  The latest mayoral election took place in 2016. The 2016 United Kingdom local elections were held on Thursday 5 May 2016 were a series of local elections which were held in 124 local councils and also saw 4 mayoral elections in England which also coincided with elections to the Scottish Parliament, the Welsh Assembly, the Northern Ireland Assembly, the London Assembly, the London mayoral election and the England and Wales Police and crime commissioners.  By-elections for the Westminster seats of Ogmore and Sheffield Brightside and Hillsborough were also held.  These proved to be David Cameron's last local elections as leader of the Conservative Party and Prime Minister as he resigned two month later following the defeat of Remain in the referendum on Britain's continuing membership of the European Union. The 2016 London Assembly election was an election held on 5 May 2016 to elect the members of the London Assembly.  It took place on the same day as the London mayoral election and the United Kingdom local elections. Richmond Park is a parliamentary constituency which has been represented in the House of Commons since 2017 by Zac Goldsmith, of the Conservative Party. Lady Annabel Goldsmith (formerly Birley, née Vane-Tempest-Stewart; born 11 June 1934) is an English socialite and the eponym for a celebrated London nightclub of the late 20th century, Annabel's.  She was first married for two decades to entrepreneur Mark Birley, the creator of Annabel's, which she helped make a glamorous success as her husband's inaugural members-only Mayfair club.  Known in London as a society hostess, during the 1960s and the 1970s, she gained notoriety in gossip columns for her extramarital affair with Anglo-French financier Sir James Goldsmith, who later became her second husband.  A descendant and heiress of the Londonderry family, her primary occupation has been as a mother of six children whose births span 25 years.  She is also an author and founder of the Democracy Movement, a Eurosceptic political advocacy group.  Her son Zac Goldsmith is the Conservative MP for Richmond Park.
Answer: Sadiq Khan