Question: Sadiq Khan is currently Mayor of London; how has this position been attained?

Context paragraphs:
London mayoral election, 2020: The next London mayoral election will be held in May 2020, to elect the Mayor of London, the position currently held by Sadiq Khan.

Sadiq Khan Shaqaqi: Sadiq Khan Shaqaqi was the second khan of the Sarab Khanate from 1786 to 1797.

Amy Lamé: Amy Lamé (born Amy Caddle on 3 January 1971) is an American-born, naturalised British performer, writer, TV and radio presenter, known for her one-woman shows, her performance group Duckie, and LGBT-themed media works.  She was appointed by mayor Sadiq Khan as London's first 'Night Czar' in November 2016.

Joe Grima (politician): Joe Grima (February 4, 1936 – February 3, 2017) was a Maltese politician, Labour Minister, broadcaster and one of Malta's first newscasters.  In the early 1970s, Grima was CEO of the Malta Broadcasting Authority.  He had a robust career in radio and television before entering politics in 1976 when he won his first election to the Maltese parliament.  He later became Industry Minister and Tourism MInister in the 1980s.  Grima quit politics in 1992 to go back to radio, but in recent years, he was Malta's envoy to the World Tourism Organization.  In May 2016, he stepped down from the tourism envoy position due to controversial comments he made about London mayor Sadiq Khan.

Mayor of London: The Mayor of London is an elected politician who, along with the London Assembly of 25 members, is accountable for the strategic government of Greater London.  The current mayor is Sadiq Khan, who took up office on the 9th of May 2016.  The position was held by Ken Livingstone from the creation of the role on the 4th of May 2000, until he was defeated in May 2008 by Boris Johnson, who served two terms before being succeeded by Khan.

Greater London Authority: The Greater London Authority (GLA) is a top-tier administrative body for Greater London, England.  It consists of a directly elected executive Mayor of London, currently Sadiq Khan, and an elected 25-member London Assembly with scrutiny powers.  The authority was established in 2000, following a local referendum, and derives most of its powers from the Greater London Authority Act 1999 and the Greater London Authority Act 2007.

Tooting by-election, 2016: The Tooting by-election was a by-election in the constituency of Tooting on 16 June 2016, triggered by the resignation of Sadiq Khan from Parliament following his election as Mayor of London.

Rosena Allin-Khan: Rosena Chantelle Allin-Khan (born 1 January 1977) is a British Labour Party politician who has been the Member of Parliament (MP) for Tooting since 17 June 2016.  Following the vacancy caused by the resignation of sitting Labour MP Sadiq Khan after his election in May 2016 as the Mayor of London, she held the seat at the 2016 by-election.  Allin-Khan was appointed as the Shadow Minister for Sport in October 2016.

Jafar Khan: Jafar Khan Zand, (Persian: جعفر خان زند‎ ‎ ) was the seventh "shah" (king) of the Zand dynasty from 1785 to 1789.  He was the son of Sadiq Khan Zand, who was removed from the throne in Shiraz by Ali Murad Khan, who had previously taken Isfahan for himself.

Sadiq Khan: Sadiq Aman Khan {'1': ", '2': ", '3': ", '4': "} (born 8 October 1970) is a British politician.  He is currently Mayor of London, a position held since 2016.  He was the Member of Parliament (MP) for Tooting from 2005 to 2016.  A member of the Labour Party, he is on the party's soft left wing and has been ideologically characterised as a social democrat.

Supporting paragraphs: Greater London Authority Sadiq Khan
Answer: directly elected