The following contains major spoilers for Room of Swords. It's recommended that you are up tp date with the comic before auditiong for this role. 

Don is a musician and gardener from Mexico in the 1950's. His powers classify him as a bard- he has the ability to alter reality through song, most often by singing. Don appears to be a kind, compassionate person who just wants to help everyone in the Room of Swords get home, even taking on the role as a leader of sorts to others. However, his friendly attitude is merely a facade- Don is an incredibly manipulative, power-hungry man who uses others to acheive his goals. Don's real motive, in short, is to regain his full power and reconstruct the whole of reality as he sees fit. He thinks of himself as a god, and is overly confident in his power. The very root of his deranged power trip lies with his regrets in not being able to save his family being killed by anomalies (presumably) however this hasn't been fully explored in the story at this point.