A rustler is a person who steals animals, especially cattle, from a farm or ranch.
Rustlers are thought of as sneaky and dishonest.
Examples:
The rustler took the cows from the farm.
The sheriff caught the rustler stealing horses.
The rustler sold the stolen cattle for money.
The rustler thought he could take the cows without anyone seeing him.
The rustler was the sneakiest person in the whole town.
The rustler always wore a big hat and a mask when stealing animals.