TV Sidekicks with Kick

Which sidekick, from television, is least content to blend into the background and simply be, well, a sidekick, but rather is unique, determined, and charismatic enough to sometimes even upstage the more central character? Which "sidekick" has the most... kick?*

*According to thesaurus.com, the meaning of "kick" is similar to zest, punch, impact, spirit, and spice.

Discuss here