The most common and most likely answer to this crossword clue is the 9 letter word SUBTENANT
I've seen this crossword clue in The Times
S
U
B
T
E
N
A
N
T
More clues leading to the result SUBTENANT
Buddy explains!
The straight part
We know that "One legally controlled by a couple of letters?" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case one legally controlled by a couple of letters? = subtenant.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 SUBTENANT mean?
SUBTENANT noun- Someone who sublets, a person who rents from a tenant.
- To sublet.