The Terrible Trivium is one of the Demons of Ignorance and a villain in The Phantom Tollbooth by Norton Juster. He represents wasting time and avoiding responsibility by performing useless tasks.
He's humanoid, nicely dressed in a beautifully tailored business suit with a bowler hat to match and, strangest of all, in what was almost certainly intended as a hint as to his sinister nature, he has no face.
He first appeared shortly after the heroes Milo, Tock, and the Humbug arrived in the Mountains of Ignorance, and initially appears friendly. He gives each of them tasks, saying that he'd let them go on in their quest if they'd help him with "A few small jobs." For Milo, the task is to move a huge pile of sand from one spot to another using a pair of tweezers to carry it over one grain at a time, for the Humbug, to dig a hole from a cliff by using a needle and for Tock, to empty a well by using an eye dropper. Eventually, Milo realizes that these tasks are a waste of time, and through the use of a magic pencil that he was given by the Mathemagician, he calculates that, at the rate they're going, it'll take them 837 years to finish their tasks. At this, the Trivium admits to his true nature, and tries to stop the heroes, but they flee, and the Trivium sets out to rouse all the other demons in the Mountains of Ignorance. In the original novel, he is presumably defeated along with the other demons when the armies of Wisdom unite to battle them. In the Chuck Jones movie, the Trivium is seemingly destroyed when Milo uses his combination of words and numbers to launch the word "Industry" at him. When it hits him, it explodes into the words "Achievement," "Work," "Diligence," "Accomplishment," and "Effort," all words whose meanings are certain doom to a purveyor of useless tasks and wasted time like him.
"Quite correct! The Terrible Trivium. Demon of petty tasks and worthless jobs. Monster of habbits. Ogre of wasted efforts. And friend to lazy and foolish people everywhere."
"What's more important than doing unimportant things? If you stop to do enough of them, you'll never get to where you're going."
"If you only do the easy and useless jobs, you'll never have to worry about the important ones which are so difficult. You simply won't have the time, for there is always something to do to keep you from what you should really be doing."
"THERE ARE SO MANY THINGS TO TAKE AWAY, AND THINGS TO BRING BACK. SO MANY HOLES TO DIG. SO MANY DOODLES TO DOODLE. SO MANY USELESS THINGS LEFT TO DO."