The Red Skull's issues with Captain America have been pretty consistent since they first met. They each fervently represent irreconcilable philosophies, plus The Skull is spitefully vengeful.

On the other hand, the relationship between Magneto and Prof. X looked nothing like X-Men no. 1 by the time Xavier bit the dust.

These examples provoke two questions from me:
  • What are some of the long-running archenemy pairings whose dynamics have changed, and why was that for better or worse?
  • Alternatively, what are some of the long-running animosities that have stayed the same, and what's given them that staying power?