Kuma

   ∩___∩
   | ノ      ヽ
  /  ●   ● | 
  |    ( _●_)  ミ  
 彡、   |∪|  、`\   Kuma──!!
/ __  ヽノ /´>  )  
(___)   / (_/
 |       /
 |  /\ \
 | /    )  )
 ∪    (  \  
       \_)

Kumā is the Japanese word for bear. And that's it. That's what this guy's deal is. He is a bear.

ヽ(・(ェ)・)ノ

Taking the Bait

               .|  
               .|  
    ∩___∩    |  
    | ノ\   ,_ ヽ  .|  
   /  ●゛  ● |   .J  
   | ∪  ( _●_) ミ 
  彡、   |∪|   |     
 /     ∩ノ ⊃  ヽ
 (  \ / _ノ |  |
  \  "  /  | |
   \ / ̄ ̄ ̄ /
      ̄ ̄ ̄ ̄

Kuma was often used to represent 2ch users falling for bait from trolls. Oddly enough, he appears to genuinely recognize the bait for what it is, yet still takes it anyway.

                             |
                             |
      ∩___∩             |
      | ノ  _,  ,_ ヽ        ((  | プラプラ
     /  ●   ● |         (=)
     |    ( _●_)  ミ _ (⌒)   J  ))
    彡、   |∪|  ノ
⊂⌒ヽ /    ヽノ  ヽ /⌒つ
  \ ヽ  /         ヽ /
   \_,,ノ      |、_ノ

                        /
                 ぷちっ   /
         ∩___∩  .   从 /
         | ノ       ヽ      /
        /  ●   ● |  (=)ヽし
        |    ( _●_)  ミ/ ` ノ
       彡、   |∪|  ノ   /
         /   ヽノ     /  ノノ
         /         /
        /        /

           ムシャ         |
             ムシャ       |
      ∩___∩              |  ぷらぷら
      | ノ      ヽ        ((   |
     /  ●   ● |         J  ))
. ((  |    ( _●_)  ミ ・
    彡、   |∪}=) ,ノ ∴
     /    ヽ/^ヽ ヽ  。
     |      ヽ \ |
     |      ヽ__ノ

         \   ∩─ー、    ====
           \/ ● 、_ `ヽ   ======
           / \( ●  ● |つ
           |   X_入__ノ   ミ   I was lured with such bait, kuma――
            、 (_/   ノ /⌒l
            /\___ノ゙_/  /  =====
            〈         __ノ  ====
            \ \_    \
             \___)     \   ======   (´⌒
                \   ___ \__  (´⌒;;(´⌒;;
                  \___)___)(´;;⌒  (´⌒;;  ズザザザ

Pedobear

Pedobear seal of approval

Westerners may find Kuma disturbingly familiar, as the 4chan meme Pedobear was derived from him. Pedobear was originally used by 4channers to alert mods to CSAM being posted, and over time became a symbol of pedophilia on the internet.

Eventually, other memes such as Spurdo Spärde and Gondola came to be derived from Pedobear, just as Pedobear himeslf was originally derived from Kuma.

Kuma's Mortal Nemeses

Nukedonald

  三|三
  イ `<             ,..-──- 、         _|_
   ̄             /. : : : : : : : : : \        |_ ヽ
   ∧           /.: : : : : : : : : : : : : : ヽ      (j  )
   /  \        ,!::: : : :,-…-…-ミ: : : : :',
              {:: : : : :i '⌒'  '⌒' i: : : : :}     _ヽ_∠
  └┼┘          {:: : : : | ェェ  ェェ |: : : : :}       lニl l |
.   |_|_|  , 、      { : : : :|   ,.、   |:: : : :;!      l─| l 亅
   __   ヽ ヽ.  _ .ヾ: :: :i r‐-ニ-┐ | : : :ノ        _
    /     }  >'´.-!、 ゞイ! ヽ 二゙ノ イゞ‐′      l  `ヽ
   ´⌒)    |    -!   \` ー一'´丿 \       l/⌒ヽ
    -'    ノ    ,二!\   \___/   /`丶、      _ノ
        /\  /    \   /~ト、   /    l \
       / 、 `ソ!      \/l::::|ハ/     l-7 _ヽ
      /\  ,へi    ⊂ニ''ー-ゝ_`ヽ、    |_厂 _゙:、
      ∧   ̄ ,ト|    >‐- ̄`    \.  | .r'´  ヽ、
     ,ヘ \_,. ' | |    丁二_     7\、|イ _/ ̄ \
     i   \   ハ∟       |::::|`''ー-、,_/  /\_  _/⌒ヽ

Nukedonald (aka. Nukedo) is an AA version of Ronald Mc Donald who encourages people to fight him. His catchphrase is "お前ら表へ出ろ"/"omaera omotehedero" which translates to "you [guys], step outside".

                                  _ /- イ、_
             ,;^,^,ヽ                 /: : : : : : : : : : : (
            ;^|, |, |, |                /: : : : ::;:;: ;: ;:;: ; : : : ::ゝ
           r|, |, |, |, }               {:: : : :ノ --‐' 、_\: : ::}
   ∩___∩ |   ( |               {:: : :ノ ,_;:;:;ノ、 ェェ ヾ: :::}
   | ノ      ヽ ! `´. ノ   、           l: :ノ /二―-、 |: ::ノ
  /  ●   ● | 入 /   ,,・_           | //   ̄7/ /::ノ
  |    ( ●_)  ミ / , ’,∴ ・ ¨           〉(二─-┘{/
 彡、   |∪|   / 、・∵ ’  /、//|  ̄ ̄ヽ
/ __  ヽノ  /        /   // |//\ 〉
(___)    /        /    //   /\ /
         /        /        / 

Pipo-kun

>>1
                    ,ィ⊃  , -- 、
          ,r─-、      ,. ' /   ,/     }     ち
          {     ヽ  / ∠ 、___/    |
   署     ヽ.      V-─- 、  , ',_ヽ /  ,'      ょ
           ヽ  ヾ、  ',ニ、 ヽ_/ rュ、 ゙、 /
   ま        \  l  トこ,!   {`-'}  Y        っ
             ヽj   'ー'' ⊆) '⌒`  !
   で    , 、      l     ヘ‐--‐ケ   }        と
        ヽ ヽ.  _ .ヽ.     ゙<‐y′   /
   来     }  >'´.-!、 ゝ、_  ~  ___,ノ
         |    -!   \` ー一'´丿 \
   い    ノ    ,二!\   \___/   /`丶、
        /\  /    \   /~ト、   /    l \

Pipo-Kun is the mascot of the Tokyo Metropolitan Police Department. He is used to reply to suspicious 2ch users with the catchphrase "ちょっと署まで来い"/"chotto sho made koi" translating to "come to the [police] station for a moment". He is a rival of both Kuma and Nukedonald.

A Japanese sign featuring Pipo-Kun.

Sources: