text: Mr Johnson, the Mayor of London, announced on Sunday that he would be backing the campaign for Britain to leave the EU.
  His intervention in the debate - made, as he termed it, with "deafening eclat" - was even said to have helped cause the pound to slide on the international money markets as traders thought it made the possibility of a so-called Brexit more likely.
  He has arguably the highest profile of any of the governing Conservative Party except the Prime Minister David Cameron, but those outside the UK may be wondering: who is he, and is that actually his hair? Read on.
  Profile: Boris Johnson
  How could 'zip wire prat' become prime minister?
  Read more about the UK's referendum on the EU
  Alexander Boris de Pfeffel Johnson, to give him his full name, was born in New York and is descended from Turkish, French and German stock. He describes himself as a "one-man melting pot".
  He first made a name for himself in journalism, including a stint as Brussels correspondent for the right-wing Daily Telegraph newspaper and editor of The Spectator magazine. His humorous persona led him to become a fixture on various television programmes, including the satirical BBC panel show Have I Got News For You.
  He still has a lucrative and entertaining column in the Daily Telegraph, in which august forum he explained the reasons for his decision on the EU.
  As a politician, he has been a Conservative member of parliament for two constituencies, Henley from 2001 to 2008 and then Uxbridge and South Ruislip from 2015.
  Lest you think he was putting his feet up between parliamentary mandates, he is also currently serving the second of two terms as mayor of London, no mean feat in a city where the centre-left Labour Party has dominated in recent decades.
  That's indicative of the position Mr Johnson has carved out for himself as one of the most charismatic politicians in the UK who has wide appeal beyond Conservative heartlands - polling has suggested that his stance on the EU referendum may sway some undecided voters.
  Just look what happens when you type his name into Google.co.uk.
  Not quite. He has previously courted controversy for his remarks about (among others) the populations of Liverpool, Portsmouth and Papua New Guinea, not to mention run-ins with his own party leadership and TV chef Jamie Oliver.
  Last October he accidentally flattened a 10-year-old schoolboy at what was meant to be a friendly game of photo-op rugby in Japan.
  But none of this seems to have affected his standing among the party faithful or the public at large. Even getting stuck on a zip-wire during the London Olympics in 2012, a sure-fire route to derision for any other politician, only enhanced his eccentric image.
  Mr Johnson finally ended months of speculation about which side of the EU debate he would back in an immaculately impromptu media scrum outside his home in North London, having reportedly informed the prime minister of his decision earlier the same day.
  He said that he had come to his decision as a result of deeply held convictions and "after a huge amount of heartache". His father Stanley, a former Conservative member of the European parliament, said that his son had performed a noble and potentially "career-ending move", ruining any chance of serving in Mr Cameron's cabinet.
  But Mr Cameron has already said he won't run for another mandate when his current one ends in 2020. Some observers of British politics point out that even if the UK votes to remain in the EU, positioning himself in the "Out" camp won't do Mr Johnson any harm with grassroots Conservatives, many of who are Eurosceptic and will have the final say in choosing a new leader.
  In this, some suggest, he is implementing his long-standing policy on cake: "My policy on cake is pro having it and pro eating it."
  No, that's Donald Trump. Also a pioneer of unorthodox political hair, but they don't get on.
  When Mr Trump commented that parts of London are "so radicalised the police are afraid for their lives", Mr Johnson retorted: "The only reason I wouldn't go to some parts of New York is the real risk of meeting Donald Trump."
  No, I've confused you now by mentioning Donald Trump. Same hair though.
  No, that's Julian Assange.
target: Foreign observers of the UK's debate on its forthcoming referendum on whether to stay in the European Union may have noticed an awful lot of fuss about the views of a man called Boris Johnson - yes, that man on the zip wire.