Diamond is often apathetic and rarely not seen eating - even in dire situations, as was the case when he had a feast with his Pokémon while aboard a Team Galactic airship that was headed straight to their HQ. He shares these traits with his Pokémon, especially so with his Munchlax. While not fat, he is much less active and energetic when compared to Pearl or Platinum, as seen when Platinum mused that every morning since the trio began traveling together, Diamond would perpetually end up being the last to get up. However, he is always serious when it comes to food and is an expert at cooking Poffins.  Diamond and his best friend, Pearl, form a comedy duo.

Diamond has a somewhat natural instinct to judge how a Pokémon feels and can be quite observant when something arouses his interest. He is driven by emotion, thus his association with Mesprit. For his skills, he is given the title of "Empathizer".

I imagine him having a rather high voice.