Calvin's Killer Bicycle, also known as the Killer Bicycle, is a recurring antagonistic object featured in Calvin and Hobbes. It is always after Calvin and chases after him. Unfortunately, it always does it when other people aren't present, so no on believes Calvin's stories of his bike, except Hobbes.
The bicycle usually pretends not to be harmful and jumps on Calvin at the last minute. Also, it is hidden somewhere (e.g. in Calvin's closet) and when Calvin comes near to it, it attacks and beats him. When attacking Calvin, it sometimes forgets that it must not reveal itself to adults, blinded by rage. This has led it to make messy tire tracks inside the house, which it is unable to remove.
It is somehow capable of ringing the doorbell of Calvin's house, as well as standing still with the kickstand up and moving without a rider on it.
Calvin's father often tries to teach him to ride the bicycle, as he himself loves cycling, but it usually doesn't work. Calvin doesn't believe his bicycle even when his parents are near him. He actually hates cycling what his father doesn't understand to. Their lessons usually ends up with Calvin screaming in horror while cycling. Hobbes once tries to teach Calvin, too. It works and Calvin balances very well, until it is revealed the kickstand is still up.
The only one who actually believes these stories is Hobbes. Hobbes sometimes laughs at Calvin, for example when he wears extra pairs of clothes to cushion his fall. He also gives Calvin ideas to stop the bicycle.
It is usually the bicycle that wins and beats up Calvin, but sometimes Calvin wins. He once jumps at his bike and ties it up to the tree, making his father puzzled, as he bought a bicycle chain to Calvin some days ago. Thanks Hobbes's advice, Calvin also puts a stick on the outer tire and pushes to deflate the tire.
The bicycle is very likely yet another product of Calvin's imagination, which tends to be a distorted view of the world around. It is also likely it came from his incompetence at riding bicycles, creating a phobia. In spite of that, it still manages to injure him quite well, meaning Calvin probably falls down from it and hurts himself badly.