Sir Bill Gammell, the founder and former boss of Cairn Energy, is to retire as Non-Executive Chairman after two and a half decades on the board of the oil and gas group.Gammell, who was appointed to the board as Chief Executive Officer (CEO) on Cairn's initial listing in 1988, stood down from that roll in 2011 to take up his current position. He will retire at the company's annual general meeting on May 15th and will be replaced by current Non-Executive Director Ian Tyler, who joined the board last summer.Tyler, the former chief of Balfour Beatty, is currently the Non-Executive Chairman of both Al-Noor Hospitals and Bovis Homes and also a board member at Cable & Wireless Communications and BAE Systems.Cairn's current CEO Simon Thomson said that Gammell "has been an exceptional leader and leaves a lasting legacy at Cairn"."His role in the company's growth over 25 years has delivered significant value to shareholders." The stock was down 1.3% at 196.2p in early trading on Monday.BC