Doodle Devil is the titular antagonist of the internet game "Doodle Devil" - which is part of the "Doodle God" series - it revolves around a similar concept to the mainstream "Doodle God" games in the fact the player gains control of an all-powerful but ultimately invisible godlike being and must create new elements out of pre-existing ingredients - as they progress the number of elements/ingredients increases.
However in-keeping with its name "Doodle Devil" revolves around the cosmic horror that is "Doodle Devil", the archenemy of "Doodle God" and a light-hearted parody of Satan, just as "Doodle God" creates so it is the task of "Doodle Devil" to destroy and bring evil upon the world.
Doodle Devil has access to almost omnipotent level powers (though he is presumably less powerful than "Doodle God") - he specialises in creating evil creatures and installing sin into the minds of humans so as to create such horrors as war, death and corruption.
In the opening scene of the game it is shown that Doodle Devil was responsible for the Fall Of Man in his dimension, resulting in a similar fate to that of the Biblical Adam and Eve (though in "Doodle Devil" it is parodied somewhat with an angry "Doodle God" quite literally kicking them out of Heaven).