The BBC has been called up on its description of Nelson Mandela as the "first black president of South Africa" on the grounds that "first democratically elected president of South Africa" should trump that.
Which made me think. By that definition, who was the first democratically elected prime minister of the UK? President of the US? National political leader anywhere in the world?
Be prepared to defend your choice for the US. The UK is workoutable if you have solid general knowledge, but I'd be deeply impressed if anyone knew the last one without Google. (Himself guessed the UK and guessed the country of the last one, but not the person)