The Demon King is a benevolent robot at the Granbell Kingdom who serves as the park's animatronic villain character, and is a surrogate grandfather figure to Shiki. Before breaking down sometime prior to the series, the Demon King takes measures with the other robots to evacuate Shiki from the planet before they all cease to function by staging an uprising against mankind upon the arrival of a human visitor, Rebecca.

The demon King should sound rough but kind and sincere.  There's no need to do a robotic tone as I will be adding an effect to the audio myself.