Diamond is the stooge of the comedy duo, with his childhood friend Pearl playing the straight man. Despite appearing seemingly dopey and slow-witted when performing his role, he is actually very perceptive. His name is often shortened to Dia, but is also called by his full name, Diamond, by Pearl when the latter is unusually serious. 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 Ginga-dan airship that was headed straight to their HQ. He shares these traits with his Pokémon, especially so with his Gonbe. 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. He also displays an ability to analyze the situation at hand - when something strikes him as illogical, he will attempt to make sense out of it. 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 Emrit.

Spoiler

For his skills, he is given the title of "Empathizer".

(Source: Bulbapedia)