What’s fun about this is that George Clooney had roles in both of them. Obviously it’s his turn in the later show as Doug Ross that made him GEORGE CLOONEY; in the sitcom, he was a mere (recurring! not regular cast!) ER tech (which makes sense – he was only 23 at the time).
The question I put to you, anonymous reader, is this: What other famous actor appeared in multiple episodes of both ERs?
(The Wikipedia link for the 80s show gives it away, so think hard before clicking.)