I've also heard that the characters of that show represent the seven deadly sins.  It's not a perfect theory, but it's kind of fun. \n\nI'll add what I remember:\n\nSquidward: wrath\n\nMr. Crabs: greed\n\nPlankton: envy\n\nSandy: Pride\n\nPatrick: sloth\n\nSpongebob: lust (don't remember why)\n\nGary: gluttony (running joke about him needing to be fed)