WWhen he emerged on the political scene in 2015, 33-year-old Mohammed bin Salman, known by his initials MBS, was given a rock star's welcome by US politicians and Silicon Valley executives.

Saudi Arabia's young crown prince had a vision for the kingdom: He planned to diversify the economy, improve public services, such as healthcare and education, and drastically reduce dependence on oil.

But nearly two years on, the world's youngest defence minister and de-facto ruler of one of its last absolute monarchies, has failed to keep pace with most of his proposed reforms.