If one party is an agent for another party, what is the counterpart role called, i.e. what is the role of the party of whom the first party is an agent, in a commercial context? In other words,
- "employee": "employer"
- "buyer": "seller"
- "driver": "passenger"
- "agent": ?
I've looked for antonyms, but this is isn't exactly an antonym. I considered options like "controlling organization" or "parent", but the first is too wordy and the second isn't specific to agency. An example in a sentence would be "Joe became an agent of the soft drink distributor. This is the only ___ for which he is an agent." The intended use of this word is in a list of roles that parties can play in a relationship, in a programming context. A compound word would be acceptable, provided that it's still relatively short.