Explanation:

- Option 1: A champion

- This suggests someone who is already known to be a winner or has a track record of success.

- It doesn't capture the surprise element that "dark horse" implies.

- Option 2: An unexpected winner

- A "dark horse" refers to someone who wins or succeeds against expectations.

- This individual or team may have been overlooked or underestimated.

- Option 3: A person criticised

- This doesn't fit the idiom.

- The term doesn't imply criticism, but rather surprise or lesser-known status.

- Option 4: Loved person

- Again, this isn't relevant to the idiom.

- Love or affection is not a component of being a "dark horse."