The big cheese is the most important or powerful person in a group or organisation.
The big cheese is coming to visit our office today - she's the owner of the whole company!
I don't want to work as a secretary all my life. One day, I'm going to be the big cheese!
If two people are like chalk and cheese, they are very different to each other.
Sarah and Alice are identical twins, but they are like chalk and cheese. Sarah is very shy and quiet and Alice is very loud and outgoing.
The Cooper's Hill cheese-rolling event takes place every year in Gloucestershire. Competitors chase a large Double Gloucester cheese down a hill, and the first person to pass the finish line wins the cheese.