Etimmu the mounted, armed and armored, immortal, D3H3 (IIRC, maybe H2?) Wraith Lord is a nasty piece of work. There's also the immortal, vampiric Blood Marshal.
I haven't seen Father Bart lately, but he was quite the mage in D2 -- although it would not surprise me if he came with severe Old Age this time around. Plus, he's as frail as an ordinary human.
It might also be noted that while most nations have a finite number of heroes, there are nations with a hero template (ex. a decent knight commander) for which they can get multiple ones.