a robber
A thief or a burglar.
A burglar is someone who goes into houses and steals things. Burglary is a crime that involves entering a building unlawfully with the intent to commit theft.
a robber
The mythical creature that steals things is called a "Kobold."
A hacker is a person that steals information from the computer. An example of this is, a hacker breaks into a bank and gets access to everyone's account and steals their money.
Biff.
Stealer is a person who steals things.
Thieves steal things to take them without permission and to benefit themselves. This behavior is illegal and can result in consequences such as fines or jail time.
In Queen's English, "bother" is an expression of annoyance. As an example, Winnie the Pooh will often say "Oh bother" when he's faced with a difficult (for him) problem. So, when Bilbo says "bother burgling", he's indicating that he's annoyed with the entire concept of it, and even more, that he's been saddled with the task.
A person who steals things from people's bags in public places is commonly referred to as a pickpocket.
Biff
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