Daleks are weird hybrids of R2-D2's, lighthouses and pepperpots. Their one goal in life is to EX-TER-MIN-ATE all humans, take over Earth until it turns into a ball of molten rock, basic villain stuff.
If you are wondering what is inside their shells, it can only be one thing: nuns. They used to be all over the place, and now, where are they? The skirtlike shape is the dead giveaway. Nuns always came in pairs, and now so do Daleks. The toilet plunger is an upgrade to nuns' traditional weapon of choice, The Wooden Ruler.