The Ittan-momen (Ittan - "one tan," or appx. 11 metres by modern standards, and momen - cotton cloth) is a youkai - specifically, a tsukumogami (an inanimate object which has gained life, usually through being used/owned for 99 years(!)). This means that the Ittan-momen boils down to naught but a long, living towel, which is famous for two reasons:
1. Appearing in a certain anime series
2. Coming out of nowhere to strangle people to death.
The Ittan-momen accomplished the second claim to fame by moving with the quickness, wrapping all eleven metres of itself around the hapless victim`s face and neck, then suffocating AND strangling them until they happened to, well, die.Sources