Professor William Arthur Roger Mullin is a former Scottish National Party (SNP) politician. He was the Member of Parliament (MP) for Kirkcaldy and Cowdenbeath from May 2015, until being defeated at the 2017 snap general election.

Mullin graduated from the University of Edinburgh with a M.A. Honours degree in Sociology in 1977. He was a Member of the Institute of Personnel and Development and also holds a Higher National Certificate in Electrical and Electronic Engineering.

He is an Honorary Professor at the University of Stirling, and lectured postgraduates on Applied Decision Theory, The Political Environment, and Organisation Change. He wrote a monthly column in The Times Educational Supplement Scotland. He is now a Founding Director of Momentous Change Ltd.

Mullen is an active campaigner against corruption in the finance system and is an ambassador for Transparency Task Force in the UK. He is also a director of the humanitarian organisation REVIVE Campaign that seeks to provide a voice to the most innocent victims of conflict across the globe.