The most common and most likely answer to this crossword clue is the 4 letter word AJAX
I've seen this crossword clue in Financial Times
A
J
A
X
More clues leading to the result AJAX
- Eleven motorists cross about origin of journey
- Hero with limited opening, king becoming cross
- Indian ruler beheaded by legendary hero
- Yes, German impressed by American guitar hero
- Koeman’s certainly in an unknown Dutch team
- Drivers keeping jack by side in Holland
- A sailor’s discussing ancient hero
- Wasting a billion in two instalments, ruin Dutch football side
- Greek hero in first part of Aeneid listened to sailors
- A vote for German 10, or Greek hero
Buddy explains!

The straight part
We know that "ancient hero" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case ancient hero = ajax.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.