Mona
   ∧_∧   / ̄ ̄ ̄ ̄ 
  ( ´∀`) < Look who's talking!
  (    )   \____  
  | | | 
  (__)_) 
    Mona (モナー) is the most guy of 2chn, if not one of the top guys of all time. He's representative of a generic Japanese person/2channel user. His friends are Moralar, Giko, and Shii.
  ∧_∧ 
 (    )
 ( O   )
 │ │ │ 
 (___(__)
This is the rear end of Mona. Note that his tail is small and round, like a bear's.
    
Mona's Origins
         / ̄ ̄ ̄ ̄ ̄\ 
          |  You guys    | 
   ∩_∩  |  have too   | 
  (´ー`) <  much spare  | 
  (   )  |  time.      | 
   | | |   |           | 
  (___)__)   \_____/ 
Mona is thought to have originated on either Ayashii World or Amezou, which were both precursors to 2ch. He looked more bearlike then, and his catchphrase was "omae-ra mo himana yatsurada nā" (おまえらも暇な奴らだなぁ), translating to "You guys have too much spare time", a saying used to remind internet users to go touch grass. This original variant of Mona is sometimes called Great Ancestor Mona (ご先祖モナー).
Then someone replied to a Mona with another Mona saying "omae mona" (マエモナー), meaning, "So do you!" or "Look who's talking!" That instantly became Mona's new catchphrase.
 
Derivatives:
Round-Eared Mona
   ∩_∩  / ̄ ̄ ̄ ̄ ̄
  ( ´∀`)< Let's Enjoy!
  (    )  \_____
  | | |
  (__)_)
Round-Eared Monas are another type of Mona, often used as background characters.
Mona's Family Tree
This thing is huge. I didn't make this, and I have no idea who half the characters on it are. It's also missing a few characters. Honestly, I'm convinced some of these are made up. Scroll around and click on the links to explore.