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Felix Hernandez
The True Hero of Once Upon a Time

This guy was the leader of the production team and personal assistant to Adam and Eddy in all areas of the show’s development throughout Season 1 to 3A.  He was able to influence them in their creative decisions and help make the story as good as it was.  The character of Felix, Peter Pan’s lieutenant, was even named after him because of how important he was.

There were other people to credit for the show’s original high quality too: studio heads like Channing Dungey, A&E’s old mentor Damon Lindelof who helped them behind the scenes in Season 1, and a host of talented writers like Daniel T. Thomsen, Ian Goldberg, Robert Hull and Christine Boylan who dropped out by the end of Season 3 (plus David Goodman and Jane Espenson, who remained to the end and usually attempted to produce quality material with sincerity). But I think Felix was the big one, since the moment he was promoted in 3B to the more hands-off role of producer rather than A&E’s personal assistant, the show took a decline in quality that it never recovered from, all the way to its recent conclusion.  It’s ironic that the last episode he served in his old role began with this happening to his namesake:

Your guiding hand was solely missed, Felix.