After years of delays, the mammoth Lucas Museum of Narrative Art is finally approaching completion in Exposition Park in Los Angeles.

Despite its looming presence, though, the museum being built by George Lucas, creator of the “Star Wars” franchise, has long seemed to lack the sort of defining mission that would protect it from being dismissed as a vanity project.

What is a museum of narrative art? And why is Lucas building one?

Even now — 15 years since Lucas first proposed a museum, and eight years after ground was broken in Los Angeles — many questions remain about an ambitious but somewhat amorphous project that is now slated to be completed next year.

There has also been turbulence as the museum nears its final approach. In recent weeks the museum has parted ways with its director and chief executive of the past five years and eliminated 15 full-time positions and seven part-time employees, including much of the education department. Lucas is now back in the director’s chair, installing himself as the head of “content direction” and naming Jim Gianopulos, a former movie studio executive and Lucas Museum trustee, as interim chief executive.

Its former director, Sandra Jackson-Dumont, had been hired five years ago from the Metropolitan Museum of Art. Her outsider’s eye and knowledge of the museum world had been expected to broaden the raison d’être for the institution so that it would do more than serve as a monument to things that Lucas has collected or produced. But as of April 1, Jackson-Dumont departed in a move that was framed as a resignation.