King Juan Carlos

European royalty has struggled to stay relevant in the modern age. One monarch who succeeded is King Juan Carlos of Spain, whose sure sense of personal and national destiny helped his country turn itself into a democracy.

That happy result was hardly preordained. Juan Carlos was born in exile in 1938; his father ceded his education to General Francisco Franco, the dictator who supplanted the royals, hoping this would encourage Franco to restore the crown. Juan Carlos was named as Franco's eventual successor in 1969, but democrats had no great expectations of him. They realized their mistake once...