Spelunking the obscure here, but . . . the great composer Edgard Varèse appeared uncredited as the head police officer in the 1920 version of Dr. Jekyll and Mr. Hyde, and it’s available to watch. I actually wouldn’t particularly recommend watching the whole thing — it’s slow as molasses but none too sweet. Also, the organ music played throughout has nothing to do with what happens onscreen.
Apart from Varèse’s bit part (he features intermittently from 1.01.20 to about 1.08.25), at least there is one over-the-top mad-scientist-drinking-a-vile-foamy-substance-and-transforming-into-a-monster scene, at 25.20, and one turning-back-again scene at 28.10. Robert Louis Stevenson’s deadpan ironic style comes off much better in the book, where it’s often laugh-out-loud funny, though the last twenty pages of his seventy-page story is full of boring, longwinded exposition, so I suppose there’s still some room for a movie version that beats out the original, the way James Whale’s Frankenstein was head and shoulders and neck bolts better than Mary Shelley’s snoozer.
It is still great to see that Varèse was in a mad scientist movie, even if the producers were too stupid to cast him as the mad scientist. (He did make it there eventually on his own, anyway).