Correct me if I’m wrong, please. I have no first hand info. The Shia feel that the head honcho must be a relative of Mohammed whereas the Sunni feel the leader can be chosen from without.
Im not sure about now. There isnt really a head honcho in either at the moment, anyone can become a shiekh in sunni and shiite and spout whatever hate they wish.
But i think you might be referring to the original split when mohammed died and there was no successor named. The shiites believed it should be a relative and the sunnis believed should have been someone else, a general or something like that. The relative in question was Ali and is a holy person for shiites.
I just did some research as i got curious:
Mohammed declared ali(his cousin) as a brother, ali married mohammeds daughter, was charged with writing quran verses that mohammed dictated and to spread the word to regions. According to mohammed he was the closest to him which is why mohammed gave him his daughter to marry. When mhammed died ali and the family were performing burial rights, and during that time one of mohammeds companions gathered many muslims and was nominated to be the leader after mohammed. He then went to where mohammed lived and ordered ali and mohammeds family pledge allegiance. mohammeds daughter threatened that she would show her hair and they left(made me laugh :D). Thus began the split. After he compiled the quran but the leaders rejected it and reorganized it but he did not reject what they did. He was later chosen as the 4th caliph but was assassinated while praying. It all gets very complicated from there.