"Speak of the devil" is the short form of the English-language idiom "Speak of the devil and he doth appear" (or its alternative form "speak of the devil and he shall appear"). The form "talk of the devil" is also in use in the United Kingdom.[1] It is used when an object of discussion unexpectedly becomes present during the conversation. It can also be used about a topic that quickly becomes relevant, such as the onset of rain or a car breaking down.
The phrase may be traced back to the 15th century Chinese novel Romance of the Three Kingdoms as 说曹操，曹操到 or "Speak of Cao Cao, Cao Cao arrives".[2]
In many cultures a different, dangerous, person or character is referenced in the phrase. In Serbian, the phrase translates to, "Speak of the wolf and he is at your door." French translates it to "Speak of the wolf and you see its tail". In Scandinavia it's "When you speak of the trolls, they're in the hallway".
Although the notion that the use of words has a power in itself is as intrinsic to the use of language as is breathing to life, the utterance, Speak of the devil....' has an illocutionary force that is necessarily independent of previous authority. The linguistic act creates the being in the act of utterance. This is a common-place in pre-scholastic societies.