First it was Mickey Goldmill "Burgess Meredith" until he died, then Apollo Creed "Carl Weathers" along with his old trainer Duke "Tony Burton". Burgess Meredith played the role of Rocky's trainer in the original "Rocky" and had a role in all the sequels. He died on 9 Sept 1997, but www.imdb.com also listed him as a cast member in the 2006 "Rocky Balboa". I have not seen this so they must have used file footage of him.
Mr. Temkin, who was a phenomenal ring announcer in the second and third Rocky movies, died in a car accident in 1982. (Source: IMDb)
Actor Doug Jones.
The character was played by actor Christopher Judge throughout the series.
Actor Brent Spiner.
No the actor that played Dumbledore in the first 2 movies died.