Dressed all in black, Elon Musk let out a roar. At last week's Madison Square Garden rally, the billionaire pointed to his black "Make America Great Again" cap proclaiming: "I am dark, gothic Maga."

Once a self-described "socialist", Musk has emerged as one of Donald Trump's most prominent and strident supporters in the final few weeks of the US election campaign.

He has made frequent appearances at rallies, handed out cheques for $1m (£770,000) to supporters registered to vote who sign an online petition, and used his platform on X, formerly Twitter, to both praise Trump and rail against Kamala Harris.