An attempt was made, in the 1930s, to turn the novels "I, Claudius" and "Claudius the God" into an epic movie. It was unfinished, abandoned when one of the stars was in a car accident, and never released. A different production of "I, Claudius" http://www.imdb.com/title/tt0074006 was very successful, released in 1976.
None of the footage was lost, and was gathered into a documentary in the 1960s, "The Epic that Never Was" http://www.imdb.com/title/tt0199498/, It can be found on BBC's four DVD set of the 1976 mini-series, and footage from the unfinished 1937 movie can be seen.
According to the documentary cited above, Laughton did have trouble with the part. Merle Oberon is shown explaining exactly that in an extended clip. But she also explained that he kept working at it. Whether or not he did get the characterization down eventually has been debated on this message board, with no consensus, and there is no finished film to show what the finished performance would be.
