I swear there was an episode though where Nelson's dad was there and it wasn't Barney. My favourite is Homer or Smithers
I like Lisa...she's had a great deal to overcome, both genetically and environmentally, yet she flourishes artistically and intellectually.
Nelson's dad, from I remember, got a bunch of bumps grown on his face which deformed him after eating a candy bar that he was allergic to because it had nuts in them. The circus took him away. That's why he wasn't in Nelson's life, lol.