LONDON — A French extreme free climber who calls himself Spider-Man and who has become famous for scaling buildings around the world climbed Heron Tower, the tallest building in London City’s square mile, on Thursday afternoon.

In images shared on social media, onlookers could be seen stretching their necks to get a glimpse of the climber, Alain Robert, as he ascended the imposing building, which is more than 750 feet tall.

Why Mr. Robert decided to scale the tower was not immediately clear, but it was far from the first time that the 56-year-old French stuntman has scurried up the side of a skyscraper.

He gained notoriety for high-profile ascents of the Eiffel Tower; the Empire State Building; the Petronas Towers in Kuala Lumpur, Malaysia; and the Four Seasons Hotel in Hong Kong, among others.