Obviously, knowledge of the subject, the ability to control a crowd and a voice that can be heard help.
Or do they? Why should the teacher know all the details? Students respond well to, "I don't know," as long as the implied, "... and I don't care," is not there too. Someone with general experience in the area will be more useful than someone without, but even the one without can be a pleasant travelling companion. If every student in the class is exploring the subject at a different pace and each is working on a different atom then specific knowledge of every atom is not needed. More on this below.
Even lower level students respond to individualised learning. Making a class of 20+ perform the same task at the same time takes a lot of time and getting them to all complete the tasks takes time. Students can sacrifice half a class or more on the alter of crowd control. That is an awful lot of the teaching time wasted ... and then we wonder why they get bored and restive! But there is no time wasted if they are working on their own atoms.
The next problem is keeping them all on task. The temptation for students is to chat, watch music videos or throw bits of paper at each other - and that's those on the masters degree! This is where a strong personality helps. Absolute silence would be oppressive and everyone needs some time out, so the teacher also needs the ability to judge the situation to optimise the amount of work. This would be different at different levels (does anyone know of any research in this area?).
Why should all teachers have the same talents, e.g. administration, creating coursework, creating materials, being a personal tutor? The name on the tin is the core quality required but some, who teach well, are better suited to one of the categories above. Are there efficiencies to be made by utilising the talents of teachers rather than insisting all are generalists? For example, I enjoy writing (I'm a gobby little female camel) and so creating coursework and handouts is a good use of my time. However, filling in tutorial forms and chasing non-attenders is both a chore for me and my personal tutees - I think my time could be better spent.
So what makes a good teacher - probably someone who is supportive, very flexible and a bit different. And how could a potential employer spot such a person? Well, all they would need to do is look at their portfolio of atoms to see where their strength lie and see how these match the needs of the organisation. However, a wide variety of atoms would indicate a wide range of interests - and that might be a good starting point.