Complex sentence: Dayyán was one of the first to claim this position however he was assassinated in Baghdad before he could attract many more than a few followers, seemingly at the instigation of Subh-i-Azal.
Split into simpler sentences: Dayyán was one of the first to claim this position. However, he was assassinated in Baghdad before he could attract more than a few followers, seemingly at the instigation of Subh-i-Azal.