The most common and most likely answer to this crossword clue is the 15 letter word STANDARD-BEARER
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More clues leading to the result STANDARD-BEARER
Buddy explains!

The straight part
We know that "Leading figure" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case leading figure = standard-bearer.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 STANDARD-BEARER mean?
STANDARD-BEARER noun- A person who carries a flag or banner (a standard).
- A person who visibly leads.