The World According to... Boring John

What are shapeshifters?

I have an idea, but I may well be wrong. So let's see what others think:

• Shapeshifters are characters that play more than one role in a novel (initially a friend to the protagonist, say, that then becomes a foe)
  
  - From the world according to Nick Daws
  
  
• Shapeshifters are a band, man!
  
  - From the world according to Google
  
  
• Shapeshifting is a change in the physical form or shape of a person or animal
  
  - From the world according to Wikipedia
  
  
• Shapeshifters are those who trim themselves to suit everybody [so that they] soon whittle themselves away
  
  - From the misquoted world of Charles Schwab
  
  
• Shapeshifters are...?
  
  - From the world according to YOU

Yes, you the reader, I want to know what you think shapeshifters are. It's important. The world according to Boring John depends on it...