(Adds background on Philbin and Sasser)
Sept 18 (Reuters) - U.S. discount retailer Dollar Tree Inc said on Monday Bob Sasser will be replaced as chief executive by Gary Philbin, the company's enterprise president, effective immediately.
Sasser will become executive chairman of Dollar Tree's board, the company said.
Philbin, 60, joined Dollar Tree as senior vice president of stores in 2001 and was named chief operating officer six years later. He was appointed enterprise president earlier this year with responsibilities for both the Dollar Tree and Family Dollar chains of stores.
Sasser oversaw Dollar Tree's $9.1 billion acquisition of Family Dollar in 2015, making it the biggest dollar store chain in the United States.
Dollar Tree's market value rose from about $2.3 billion to $19.8 billion since Sasser became CEO in 2004, the company said. Sasser joined the retailer as chief operating officer in 1999. (Reporting by Vibhuti Sharma in Bengaluru; Editing by Sai Sachin Ravikumar)