Diamond I took the usual action, call myself Mike (self explanitory if you've read my username) with my best friend who also still plays Pokemon (never too old!) is what my rival is named after, which is Saul.
However, in Platinum, I used my nickname (Waffle) and my rival became a newcomer which I envy in real life. Called David B (B for Boreanaz), I want to rival him, for I wish I was as hunky as that guy. Damn he's too attractive.