Zero is a legendary Reploid warrior and the protagonist of the Mega Man Zero series. Once a feared Maverick Hunter, he awakens in a dystopian future where humans and Reploids are oppressed by Neo Arcadia. Despite his past as a ruthless warrior, Zero is a calm, stoic, and highly skilled fighter who carries a deep sense of duty and responsibility. He is fiercely independent, rarely showing emotions openly, but his actions reveal his loyalty and strong moral compass.

Throughout the series, Zero is a symbol of resistance, standing against injustice with unwavering determination. Though he rarely speaks more than necessary, his words carry weight. He values his allies but often prefers to fight alone, burdened by his past. Despite this, he is deeply compassionate beneath his hardened exterior.

-Zero isn’t overly robotic—his voice should sound natural, not monotone.
-He doesn’t waste words, so his lines should be delivered with a sense of purpose.
-Think of a warrior who’s been through countless battles but never loses his resolve.

While there isn't an official English dub for him in the Zero series, you can use his Japanese voice as a reference. Here are some links to the official Mega Man Zero audio drama series that showcases their voices a bit better - 

Link 1 - https://www.youtube.com/watch?v=go4GOQTpHbY

Link 2 - https://www.youtube.com/watch?v=8Kx2o9RTrq8

(Side Note: The person who is chosen for Zero, will also be chosen for Omega.)