Steve Ells, Starbucks
 Steve Ells has been named the sole chief executive officer of Chipotle Mexican Grill.

DENVER — Steve Ells has been named the sole chief executive officer of Chipotle Mexican Grill, and co-c.e.o. Monty Moran has stepped down from his role and board seat, effective immediately, the company announced Dec. 12. Mr. Ells, who founded Chipotle in 1993, also will remain chairman of the board. Mr. Moran will retire from the company in 2017.

“Given the ongoing challenges facing the company, the board felt strongly that it was best for Steve to resume leadership of the company going forward,” said Neil Flanzraich, lead director of Chipotle’s board. “This will ensure that his high standards for the guest experience and his unyielding commitment to the company’s mission are top priorities.”

Monty Moran, Starbucks
Monty Moran, former co-c.e.o. of Chipotle

Mr. Ells was chairman and c.e.o. of Chipotle from 1993 until 2009, when he and Mr. Moran became co-c.e.o.s. Going forward, Mr. Ells will oversee strategic initiatives, innovation projects and operations for the company’s more than 2,200 restaurants in five countries.

“I’m very much looking forward to relentlessly focusing on ensuring an excellent guest experience, removing unnecessary complexity from our operations, championing innovation, and pursuing our mission of making better food accessible to more people,” Mr. Ells said. “I’d also like to thank Monty for his extraordinary contributions to Chipotle over the years. Monty inspired us with his vision for an enlightened people culture, and I wish him the best as he retires from the company.”

Mr. Moran’s departure follows the company’s toughest year as it struggled to recapture traffic and sales in the wake of a food safety crisis. In the past year, Chipotle’s shares have tumbled by as much as 35%, while efforts to regain consumer trust including new food safety measures and the company’s first-ever loyalty program have been slow to resonate with customers.