Mixing games and official manga, Ridley is intelligent, powerful, vicious, and a goddamn space dragon, but also shows a truly "human" capacity for evil. Ridley ate a girl's parents in front of her. He are them and he later taunted her about that. He tells her that all that's left of her parents is him, now. And before he ate them he used the girl's sense of childhood innocence to try to brutally murder her. He even gleefully expressed his intention to slaughter her adoptive family and force her to watch it all over again, after tricking some of them to join his side with the help of Mother Brain.
And in addition to that he is a military leader with genuine tactical abilities. He keeps getting brought back because the Space Pirates don't have a leader as effective as Ridley. He isn't always going to be their #1, but even when bigger fish step up to take over he's indispensable as a leader and a weapon. And that's another thing, death won't stop him. He's been defeated and straight-up killed several times, but he keeps finding ways to either come back or be brought back. As a cyborg, as a clone, as a cloned cyborg, as part of a twisted, nearly unkillable virus hivemind thing that took the creation of one of the most dangerous bioweapons in the galaxy to try to wipe out.
Ridley is capable of putting up a fight on a physical and psychological level against some heavy-hitters, even whole teams. He's got a twisted mind that compliments his massive amounts of muscle, making him something a writer can use for more than just having a giant space dragon wrecking shit. Now if he could just fit in regular comic panels.