"Compelling backstory" refers to a character's past that is interesting, captivating, and can evoke strong emotions in the audience. It adds depth and makes the character more engaging. Full definition
Around her, characters played by the likes of Riz Ahmed, Diego Luna and Donnie Yen all bring compelling backstories to the table. (timeout.com)
But Erik Killmonger, the character Jordan portrays, has a much more compelling backstory, and the 30 - year - old actor absolutely shines in the trailer, effusing rage while bringing a grounded humanity to make the supervillian, in such a short look, already feel sympathetic. (etonline.com)
Ragnarok gives her a very compelling backstory and connection to Thor's journey, so as he's going about his adventure, she's doing the same, until their trajectories eventually bring them back together for the final battle. (io9.gizmodo.com)