Thatguy62

So, Dark Knight Ingus.

While any of the four Warriors of Light in Final Fantasy III can become Dark Knights, Ingus stands out for a few reasons. The two in particular:

• His background

In the unused text for Final Fantasy III, almost every area has a some form of unused text. A lot of them are interesting, showcasing party dynamics that are underutilized or just plain non-existent in the final game and scenarios that would have diverged from the original. Falgabard's unused text is interesting for a different reason though: the main focus of the skit is that Ingus experiences deja vu upon arriving in the covert village, leading the party to speculate that he was born there. While Ingus is initially hesitant, he eventually reveals that he wants to return to the village once more and learn to master the Dark Blade (without relying on the crystal's boons).
So yeah, it is very likely that at least one of Ingus' parents was a Dark Knight

• His role

Final Fantasy games tend to have parties of four prominent characters. The four tend to have vaguely similar temperaments: The hero is heroic (shock), one of the party members is significantly empathic and a third is either gruff, serious or both to some extent (the fourth is a bit of a wild card. Closest is an association with animals/summons, but that's arguable to an extent).
This is especially pronounced in the Memory of Heroes novelization. Memory of Heroes is not a 10/10 novel, but it has some fun and interesting ideas. One of those is the implication that the Warriors of Light reincarnate or inherit the wills of their predecessors. In Ingus' case, he's clearly a successor for Zauver, given how he's more sarcastic here. However, under this setup, he's also a successor to Ricard... Or perhaps Leon, who Ricard gives his light to.
While this idea is strictly in the Memory of Heroes continuity, similar ideas or just acknowledgement of these roles is not impossible.

More thoughts on this later.