As the president of that academic society, he runs the annual conference.
The meeting began with an address by the chairman.
会長 is a formal title for the head of an association or society, often used in official contexts. 主宰者 can be used more broadly for anyone who takes charge of a group or event, not necessarily an official title.
campaign manager
Compound of 主宰 (shusai, 'presiding over, organizing') + 者 (sha, 'person'). The term 主宰 itself is composed of 主 (shu, 'master, main') and 宰 (sai, 'superintend, manage').