The QA engineer is a test engineer, but he/she does more than just testing.
The good QA engineer understands the entire software development process,
and how it fits into the business approach, and the goals of the organization.
Communication skills and the ability to understand various sides of issues are important.
The QA engineer is successful, if people listen to him/her, if people use his/her tests,
if people think that he/she is useful, and happy doing his/her work.
I would love to see QA departments staffed with experienced software developers who would coach development teams to write better code. But I've never seen it. Instead of coaching, the QA engineer tends to be a process person.