Just a reminder that Boris Johnson is not an elected leader.
Plus it is inaccurate, he was elected, against Jeremy Hunt, Michael Gove, and other candidates in the Conservative Party Leadership race. Voted on by MPs who the public themselves feel were qualified to represent them in a representative democracy.
I have no love for Boris Johnson (nor the Conservative Party itself). But this kind of "not a democratic leader!" line is simply spreading misinformation about how the UK's system of government works. You vote for MPs, MPs vote for stuff on your behalf, and in this case they voted for the leader of their party (and now the government).
It should also be noted that the UK doesn't have a ruling king and it doesn't have a president. The PMs power is a lot more curtailed than some other countries that do, and they need to go back to Parliament to accomplish much of their agenda (and are equally subject to the law). If they lose their voting majority, they're hugely neutered.