The Proto-Indo-European word *h₃rḗĝs
Word *h₃rḗĝs
Meaning ruler, king
See also Proto-Indo-European: *h₃reĝ- ‘to extend, to stretch’

Comments
Mallory J.P. and Adams D. (2006)

Other words that might be of interest
*reg- ‘move in a straight line, rule, guide’, *deik̂- ‘rule, canon, measure’, *h₁esh₂ós ‘master’, *hₐēgos ‘shame’, *tkeh₁- ‘rule’, *wesu- ‘excellent, noble’, *w(n̥)nákts ‘leader, lord’, *(p)k̂órmos ‘shame, grief’, *dom(hₐ)unos ‘master’, *hₐeĝós ‘leader’, *koryonos ‘leader’, *potnihₐ- ‘mistress, lady, wife’, *tagós ‘leader’