I'm in a similar situation to crodjer, in that I am struggling with a word to describe a concept.
In his case, he had a job, for which some people are responsible, say: a, b, c, d and e. In my case, a can elect one or more proxies to act on his behalf, say: f and g; similarly, b could elect g and h as his proxies.
I'm happy with the term 'proxy' for the person the task has been delegated to, but I wonder what the reverse term is, i.e. in the example above, if g is a proxy of b, what is b to g?