The OB Director
The outside broadcast director is the person who makes the show happen minute to minute. S/he is the person who co-ordinates all the staff and gives instructions to everyone as the show progresses.
As in other types of production, the director is often confused with the producer but the jobs are quite different. While the producer oversees the production and may make general requests during the show, the director is the one who puts it all together. The producer has the plan, the director implements the plan. Having said this, these two roles can blur together and in many situations it's the same person.
The director gives instructions to virtually every staff member, from camera operators to the vision switcher. In some cases other directors take some of this responsibility (e.g. VT director), but it is important for the director to have a good understanding of all OB positions. The more s/he can empathize with each operator the better their direction will be.
The director and vision switcher have a particularly close working relationship. The switcher acts as the director's hands and fingers, implementing transitions and compositions to turn the director's vision into reality. In smaller OBs the director might do their own switching.
Fast thinking and confidence are essential. There is usually little time to ponder and decisions must be made very quickly.
The OB director epitomizes the idea of human multitasking. More than any other position, the director must be able to concentrate on several things at once. At the same time as thinking about what's currently happening online, s/he is planning the next shot and might be hearing a report from the VT director, conversing with presenters, consulting with the producer, and doing a whole bunch of other things.
It helps a lot if the director has a good knowledge of the subject matter. For example, if the OB is covering a sports event the director should know the rules of the sport well enough to provide viewers with all the relevant shots and other material. S/he should also know the main players, be aware of any topical issues, etc. Basically, the director should be able to think like a viewer and know what they want to see.
Watching a good OB director at work is like watching a master symphonic conductor. It is a highly skilled position reserved for those at the top of the game.