The most common and most likely answer to this crossword clue is the 8 letter word ACHIEVER
I've seen this crossword clue in Financial Times
A
C
H
I
E
V
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R
More clues leading to the result ACHIEVER
- What's central to teaching, always, for high flyer
- Successful person a Greek character always follows
- Perhaps clever pupil's claim takes in head briefly
- First lady to occupy chair, unusually successful person
- A character from Athens, always one doing well
- A Greek character’s always a success story
- Successful chap running European archive
- One gets on elaborate chair occupied by lady in garden
- Bill given greeting, always someone deemed a success
- High-flier given a cold greeting at all times
Buddy explains!

The straight part
We know that "Successful chap" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case successful chap = achiever.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.
What does ACHIEVER mean?
ACHIEVER noun- One who achieves something.
- One who tends to succeed; a winner.