Definition of "Musketeer"

This was the rock that Musk and his Musketeers planned to build their company on.

2014, Charles Morris, "The early days of Tesla", Charged: Electric Vehicles Magazine, Issue 14, June/July 2014, page 62

Mr Vance comes across as a “Musketeer”, someone who believes in Mr Musk’s power to reshape the world.

2015 July 4, “Fortune favours the brave”, in The Economist