Influencer
The influencer does exactly that, influence.  Always focused on the goal at hand, the influencer will be the middle man/woman who will shoot for a win/win outcome where there are opposing sides on a project.  In my opinion, this role almost requires skills very closely resembling that of a parental figure. 
Strategist
Here is the person that will make a map of how to get from point A to point B while always having a clear understanding of the client's wants, needs, and concerns.
Partner
In my mind, I picture the Partner being the bridge between the client and the team.  The partner will keep communication open and flowing between the two parties.  He or she will make sure that the goals are clear and that the client is getting what they've asked for.
Technical Expert
We live in a world filled with technology, half of which most of us don't understand.  This expert will handle all the tools that will send your company soaring.  The key to an extremely useful technical expert is being able to translate all the technical jargon into English for those of us who could brush up a bit on the tech terminology!