The most common and most likely answer to this crossword clue is the 4 letter word IGOR
I've seen this crossword clue in The Guardian
I
G
O
R
More clues leading to the result IGOR
- Russian typically with stake in Iran
- Prince, villain having ousted a king
- Sung prince, I succeed king
- King cobra kills every other Russian
- Tax collectors once full of energy
- He often helps a mad scientist dig for missing heads
- I depart right after the operatic prince
- Lab assistant regularly sampled king cobra
- Operatic prince to leave embraced by one king
- Taxman nips attempt to become doctor’s assistant
Buddy explains!
The straight part
We know that "He often helps a mad scientist" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case he often helps a mad scientist = igor.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.