Muriel is one of our main LIs. He is a big man, 6'10" in height. He is very shy, and introverted, anxious in public. He prefers being alone and not speaking to anyone unless absolutely needed or he trusts them 250%. He deals with a lot of anxiety and PTSD too. This is Muriel's sprite as a kiddo. He was still shy, introverted and anxious, but he did speak a tad bit more than he does as an adult. He speaks with a lot of pauses, as if in hesitation that something bad would happen. He hates confrontations and fights. 

Voice-wise, I'm thinking a male adolescent voice. Like someone who just hit puberty and their voice hasn't developed fully yet.