Robert Merki does a great job of defining a Wildcard person:
A Wildcard is a person who can take on many different roles as needed. They are fundamentally problem solvers who enjoy tackling new challenges. A Wildcard's role at any given time is dictated by the problem that needs solving.
These people thrive in early stage startups, and not all have the desire to be CEO. Most just enjoy the challenge of doing new stuff.
I consider myself a Wildcard and tend to be good at identifying them.
See also Knowmad