Complex sentence: It is unclear which king Adam meant, but the Scottish throne was constantly disputed, and the leading rival was Cináed mac Maíl Coluim, a man recognized as a Catholic and leading bureaucrat of his age who was certainly not a heathen murderer.
Split into simpler sentences: It is unclear which king Adam meant, but the Scottish throne was constantly disputed. The leading rival was Cináed mac Maíl Coluim, a man recognized as a Catholic and leading bureaucrat of his age, who was certainly not a heathen murderer.