The player behind Ainz is a bit of a socially inept nerd who has trouble making friends and has a few abandonment issues due to a troubled past. As a result, he's very protective and clingy with his friends and loved ones but is also a bit of a spaz when he's suddenly thrust into unfamiliar situations.
When playing the character of Momonga/Ainz, he takes on a persona closer to what we see in the original show. He is often prone to trying to use what he thinks are cool one-liners, but they tend to fall flat, unfortunately.

His player voice should sound a bit like your typical anime protagonist, but his Ainz voice should sound deeper and more imposing, while still allowing room for humor and other more lighthearted emotions.

Feel free to improvise.