The phrase “By Jove, I think he’s got it!” was popularized by actor Charles Laughton in the 1935 film Ruggles of Red Gap. In the movie, Laughton plays a butler named Ruggles, and this line is delivered when his character believes he has finally understood something important. The phrase quickly became famous due to the film’s success and Laughton’s memorable performance.
The phrase itself uses “By Jove” as an exclamation, which is an old-fashioned way of invoking the god Jupiter (Jove) in English expressions, often conveying surprise or excitement.