Hi Sabina I’m Arabian Send me if you want something in Arabic

Unfortunately, قام can have (too) many meanings and usages. So, everything may depend on the context. Still, as far as I know, قام is not a sister of کان. And, as I would interpret مؤسس as "mu'assis = founder", it should not be accusative if إدريس himself is the founder (as I suppose). I wonder whether you could also have used کان or صار instead. In that case the accusative of the predicate noun would be compulsory. I feel at home with classical Arabic grammar, but I am not a native speaker. So, hopefully, some educated Arabic native speaker would help us shedding more light on this...