Although he has yet to reveal his future plans, Collister is expected to concentrate his efforts on Creative Matters, the creative consultancy he launched in January 2000.
When he joined EHS Brann in 2001, Collister's above-the-line experience made him a surprise choice for the role. He had previously worked for both Ogilvy & Mather and BMP DDB and had won several awards, including a Cannes gold.
During his stint as the creative director and vice-chairman of O&M, Collister was responsible for the creation of the new-media arm, O&M Digital. Under Collister's leadership it won the first Cannes Cyber Lion award for the CampaignLive website.
Earlier this year, Collister ran for the presidency of D&AD, but was defeated by Leo Burnett's executive creative director, Nick Bell.
EHS has yet to name a successor for Collister, although an announcement is expected later this month. It is believed that the agency will appoint two people to the role. Collister leaves behind a team of creative directors including Trevor Chambers, Patrick Bagley, Brian Storey and Xanthos Christodoulou.