Ranger was created with nearly only negative personality traits and was initially devoid of any empathy or kindness. He has a strong inferiority complex toward humans which leads him to act with sadistic glee at their despair. He pretends like he treats humans dismissively, but in truth he pays a lot of attention to towards them; Going as far as collecting clothing from dead participants to wear for himself.  He usually calls participants 'bastards.'

Ranger's original Japanese name, "トト・ノエル, Toto Noeru" is a pun on 整える,' Totonoeru' literally means "to arrange; to put in order." VGperson named him 'Rio Ranger' in their translation to make up for the pun; as in 'rearranger.'

To go more in-depth on his voice:

Rio Ranger is. Evil bastard. He’s another character who needs to have an incredible range. This guy is intentionally malicious even though he speaks with a carefree tone. A definite villain (at least, so far). His lines should therefore take on a whole different tone/meaning. A lot of them are said with a bubbly, bouncy kind of energy, yet include a sinister underlying tone; he also mimics the voices of certain characters as he uses little pop-up expression cards. He’s cruelly mischievous, knows exactly how to get under people’s skin, and has an incredible amount of disdain for humans //spoilers// which turns out to be because he’s envious of them. He’s similar to Miley in the sense of how they both have this dark, unmistakably evil aura whilst they act ‘nicely’; but the difference is that Miley has poise and (feigns) grace, whilst Ranger goes full-out feral at times, and his composure switches at the drop of a hat. You never know what to expect from him; but it’s never anything good.

He & Miley also both revel in the suffering of others, and have egotistical tendencies; in this case, Miley seems to have this ego because she knows she’s capable of doing anything to get what she wants, and Ranger seems to think he can get away with anything. These two things might sound similar, but there’s a drastic difference in how it affects their thoughts and actions.