By (preposition)

1. Used to indicate the agent performing an action
2. Indicating the means of achieving something
3. Used to indicate the amount of something
4. Indicating the method or manner of doing something
5. Indicating a deadline or the end of a particular time period

Origin:

Old english bī, from germanic *bi, from indo-european *bʰi, *bʰe 'around, at, near'

Examples:

1. The book was written by John.
2. She fixed the car by herself.
3. He won the race by training hard.
4. The soup can be served by the ladleful.
5. We'll be back by noon.