The most common and most likely answer to this crossword clue is the 8 letter word TRIUMVIR
T
R
I
U
M
V
I
R
More clues leading to the result TRIUMVIR
Buddy explains!

The straight part
We know that "member of a ruling group" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case member of a ruling group = triumvir.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 TRIUMVIR mean?
TRIUMVIR noun- One member of a triumvirate