Allegiant Air (usually shortened to Allegiant) is an ultra low-cost U.S. carrier that operates scheduled and charter flights. It is a major air carrier, the fourteenth-largest commercial airline in North America.

Allegiant was founded in 1997 and is wholly owned by Allegiant Travel Company, a publicly traded company with 4,000 employees and over US$2.6 billion market capitalization in 2016. The corporate headquarters are in Summerlin, Nevada, a suburb of Las Vegas
From Wikipedia