Graphic design managers are rarely C-level people in product companies (except for the entertainment industry). The title is usually either Art Director or Chief Creative Officer.
You could use one of the titles in this hierarchy:
Lead -> Manager -> Director -> Vice President -> President
Each of these titles (except for president) is also sometimes preceded by "Senior", depending on experience level and influence.
The most common titles are Art Director, Design Director or Creative Director.
I would say graphics designer as normal graphics designer, and for lead or manager of these designers i would go for - Principal Graphic Designer - as they are leading the pack by example - this are the norm title in EU.
I'd say Chief Creative Office, however Chief Graphics Officer is in use, too.