Dudbears are a race of creatures from the Playstation game Legend of Mana. They live mostly in Lumina and the Ulkan Mines. They are important in a few quests, mostly the ones involving Roger's cult (The Diggers) or Lumina (everyone who has played the game remembers the lamp-selling quest).
Dudbears make up the majority of the Diggers. In fact, they make up all of the members, with the exception of Roger himself (and Roger's pet dog, Putty).
Dudbears who are not members of the Diggers live in Lumina, and...do stuff there. It's not really explained. They like lamps, though!
As mentioned above, there is a lamp-selling quest, where you have to sell lamps to Dudbears. Below is a listing of all the words you learn (Basic Dudbear), while on that quest.
Dub: Hello, Yes
Dud: Good-bye, No
Bub?: Huh?
Gak: Displeasure (as in "I'm displeased with you!")
Duba: You
Duda: Me
Dubba: Friends
Bubu: Dudbear
Gugu: Non-Dudbears
Da: Light and/or Stars
Ba: Night
Dada: Please
Dadda: Lamp
Dubababa: Many and/or Very
Du: Little
Baba: Music
Occasionally, you'll come across people who use words that you don't know (mostly Pokiehl). I have no clue what they are saying. You can, however, drag out words (Gaaaaaaak!, Dubababababab!), which just means more of whatever the word is.