The Bogeyman resembels a large rat like creature with the ability to transform into a swarm of maggots and enter its own dimension at will. The Bogeyman is a monster that would hunt down, kidnap, and imprison children in his bog world that it perceived as "Naughty" (ei: children who were disobedient) even going after Martin, Diana and Java because they aren't technically adults and at times disobedient.
In it's debut episode It Came from the Bog it was accidentally freed by a young girl when she opened a book it was imprisoned in (and subsequently grabbed and imprisoned herself by the Bogeyman) warranting investigation from the Center. Arriving on scene Martin, Diana, and Java arrived just in time for the Bogeyman to grab another child finding it's book they read it and discovered what it is and why it's doing this.
Using this information to their advantage they set up a trap using more children as bait, while the Bogeyman was unable to grab more children and the Team unable to grab it, they did force it to open a portal to his bog world and rescue the children it already kidnapped and subsequently escaped. Realizing the book contains information on how to defeat the Bogeyman they consult it to find the last page missing, Diana searches the library to find the page while Martin and Java holds the Bogeyman off.
Diana arrives with the last page and reveals that the Bogeyman has to be reimprisoned in its book, with that Martin Simply opens the book while the Bogeyman is charging him and thus forces him inside then locks the book shut.
The Bogeyman would later escape Center Custody in Germs from Beyond (its unknown how it got out of it's book but it's possible that the Center let it out to study it). The Center tried to contact Martin, Diana and Java to recapture it, unfortunately they had come down with a unidentified illness (later revealed to be food poisoning) and were subsequently quarantined in the center.
Naturally fearing the worst with all the nasty stuff they've come into contact with the trio fears that they will be executed to prevent the desease from spreading. Unfortunately they are soon hunted by the revenge seeking Bogeyman and are chased throughout the center until they finally lure it into a prison cell where M.O.M. blasts it with a shrink ray reducing it to a harmless action figure sized creature.