5. Anto Korragan
Another underdeveloped character who would benefit from having her backstory be more interacted with is Aria T'Loak - the Asari crime-whizz you talk with a couple of times on Omega. Korragan is one of her most trusted advisors, and rather than go down the easier route of having Aria be someone who's up for a bit of space adventuring, instead Anto and his cross-mingling with Liara and Feron would be a more interesting angle. You can actually talk to Korragan as he's stationed next to T'Loak in the Afterlife club, but there's far more to him than meets the eye. There's even a moment in his four-issue comic arc where instead of letting the various factions on Omega continue to battle each other, he takes it upon himself to attempts a truce, in theory allying them all towards Cerberus, and although in the ensuing battle he does get brought down, it doesn't mean that's how it has to go.