Han Solo hardly has many scenes in A New Hope, ESB and ROTJ without Luke or Leia. The major exception is that scene added in the Special Edition where Han Solo meets Jabba the Hutt in the Special Editions and of course when Han shoots Greedo (don't care personally if it's first/at the same time/or just after).
So one can argue that the character is largely defined by his interaction and connection to the latter two.