Originally Posted by
Joop312
Archimonde is way, WAY stronger than Arthas in his human and/or Deathknight form. I mean, come on, he is the field commander of the Burning Legion, he was the commander in the War of the Ancients, where he even killed Malorne (father of Cenarius). D'you think a Paladin or even Deathknight for that matter, can kill him, even though it was Arthas? And Archimonde was one of the three Eredar (before corruption) leaders (others being Kil'jaeden and Velen, as already said above) which isn't a very easy rank to obtain, since the Eredar are a brilliant race.
Tauer is right, Tales of the Past is uncorrect at some points of lore, since Archimonde, Velen and Kil'jaeden were good friends. Kil'Jaeden did look up to Velen as his brother, but appart from that fact, they have nothing else in common.
All this information can be found on Wowwiki and in the novels "Rise of the Horde" and "The War of the Ancients Trilogy".