Trustworthy - they will have access to sensitive information.
Articulate - they will communicate on your behalf.
A good dose of common sense.
Comfortable in the role of follower but not a pushover, they will be helping maintain your boundaries.
Willing to do mundane repetitive tasks, content in the knowledge that they are freeing you up.
Consistent, calm and predictable.
Process oriented - help keep things working smoothly.