Gage Skidmore [CC BY-SA 3.0 (http://creativecommons.org/licenses/by-sa/3.0)], via Wikimedia Commons
President Donald Trump is now the most-followed world leader on Twitter, having bested Pope Francis during the weekend. Trump now has 40 million followers on his @RealDonaldTrump account, slightly more than the combined total of Pope Francis' @Pontifex accounts in various languages. The numbers are tracked by the website Twitplomacy. However, both accounts are likely followed by a fake "bot" accounts as well as by accounts that are no longer used.
Former President Barack Obama has more followers than Trump, but he's not counted in this as he is no longer the president.
While Twitter has only really been around for the last two administrations (although it was created during the last part of the George W. Bush administration, it was not really popular until the Obama era), Trump has adopted a much different approach to the social network than Obama. Trump retained the use of his personal account (the @realdonaldtrump handle) as well as the @POTUS official account. Trump has announced many new policies on Twitter (such as the ban on transgender soldiers), surprising even his advisors.
Source: Town Hall