He's basically a decently-important character from Marth's games. Mostly he's notable as the progenitor of the "rugged Mercenary who's usually pretty great as a unit" that characters like Saber, Gerik, and Gregor followed in later games.
Ogma was an ex-slave gladiator, so his fighting style is very survival-focused and often dirty, as his time as a gladiator instilled in him that he needed to fight to kill, honor be damned, or it'd be his life taken instead. Plot-wise he's less important than Mar, Caeda, Tiki, Jagen, Minerva, and Merric as far as playable characters go, but a good cut above the rest of the others, given his ties to Caeda and him looking after Yuliya and Jubelo in the sequel. And the fact that Navarre got in over him in Warriors was a great injustice.
Mostly I just found it funny that of all the Fire Emblem characters, he placed highly enough to be counted. Ike was the only other one to place.