The most common and most likely answer to this crossword clue is the 5 letter word OBAMA
I've seen this crossword clue in The Guardian
O
B
A
M
A
More clues leading to the result OBAMA
- Old lady chasing old boy and a former leader
- Former leading man gets old by degrees
- Nobelist in job, a man avoiding extremes?
- First to admire Mr Aneurin Bevan, our revolutionary 5 reformer?
- Old US state, not in the style of 12
- It’s zero degrees for the man at the top
- Michelle raised Sam, a boy with some deficiencies
- Airline breaches order by American president
- Airline circles morning after old ex-President
- Head of state getting round more than half the state
Buddy explains!

The straight part
We know that "the man at the top" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case the man at the top = obama.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.