Do you know who your real customer is?

I was reading Seth Godin today and found a post that spoke to my experiences running an agile team over the past few years.

His statement was, "If you are working hard to please the wrong people, you'll fail."

My team builds tools for internal use. I've struggled to figure out which customer I should be please. Should I be trying to please the testers who use are tools? Should I be trying to please the test managers? Should I be trying to please the dev managers? Should I be trying to please my boss (hard to go wrong there)?

At various points, I've emphasized one customer over the over. And it has changed over time. It's a source of tension for myself, and to a lesser extent for my team.

Which customer are you trying to please? Is it the same all the time, or does it change with the wind?