Clue: Mistaken for a monster, out­spoken scientist drops initial interest (12)
Answer: FRANKENSTEIN
Explanation: Definition: Mistaken for a monster
**FRANK** ("outspoken") + **E**(i)**NSTEIN** ("scientist" drops [initial] I(nterest)) 
 
 
*"Mistaken for a monster" refers to the fact that many people think that the monster was called Frankenstein, whereas it was its creator that bore that monicker.