To exercise sovereign power, to rule as a monarch.
He reigned in an autocratic manner.
To reign over (a country)
To be the winner of the most recent iteration of a competition.
To be a dominant quality of a place or situation; to prevail, predominate, rule.
Silence reigned.
Currently ruling or holding a position.
The reigning world heavyweight champion said he'd defend his title once more and then retire even if he won.