Concept:ECOWAS was formed under the Nigerian leader in power when the founding treaty was signed.Explanation:Nigeria and Togo held a bilateral meeting led by General Yakubu Gowon of Nigeria and General Gnassingbé Eyadéma of Togo.That meeting led to trade agreements between the two countries in 1972.The plan later grew into the Economic Community of West African States.The ECOWAS treaty was signed in Lagos on May 28, 1975, while Yakubu Gowon was Nigeria’s Head of State.Therefore, the regime during which Nigeria spearheaded the formation of ECOWAS was that of Yakubu Gowon.Answer:Option C: Yakubu Gowon.