LAS VEGAS (AP) — The parent company of Allegiant Air says its chief executive has resigned and that chairman and former CEO Maurice Gallagher will return to lead the budget airline.

Allegiant said Thursday that John Redmond resigned as CEO and a director of the Las Vegas-based company, effective immediately. The company did not say why he left.

Shares of Allegiant Travel Co. rose 4% in morning trading.

Gallagher, who has played a role in several low-cost airlines, became Allegiant’s majority owner and joined the board in 2001. He was CEO from 2003 until last year. He oversaw a period of strong growth, as the company built a fleet of more than 120 planes and added more routes.

Allegiant primarily serves leisure travelers heading to vacation destinations such as Las Vegas. Like rivals Spirit and Frontier, the airline charges low base fares but generates revenue from fees on extra charges. Besides the airline, Allegiant is building a resort in Charlotte Harbor, Florida, that is scheduled to open in the fourth quarter.

The company has reported $144.6 million in profit during the first six months of the year, compared with a loss of $3.5 million in the same period last year.

Redmond joined Allegiant’s board in 2007, served as president, and took over as CEO last June after a career in the hotel business, including high-level jobs at MGM and Caesars World.