Olympic athletes Buster Crabbe and Johnny Weissmuller did quite well in the movies.
Burt Reynolds was an All Star Southern Conference half back with Florida State before his TV and movie career.
Shaquille O’Neal, Dennis Rodman, Kareem Abdul Jabbar, Wilt Chamberlain and Victor MacLaglen {Spot the odd one out: one of these men went six rounds with Jack Johnson in an exhibition bout - but who?}
I realize this may not fit the OP’s question, since the word “Actors” was in the question, but:
Joe Namath was in a 1970 movie called “C. C. and Company,” one of the many B biker movies out int hat time frame, with Ann-Margaret.
But again, a lot depends on your personal definition of “actor.” 
Well, have been plenty of athletes who appeared in films (e.g., Roger Maris and Mickey Mantle in Safe at Home) but who never succeeded as actors. I don’t think they count under the OP.
I’ll add [URL=“http://www.imdb.com/name/nm0732079/”]Paul Robeson[/URL-. His movie credits are sparse, but he was a very successful stage actor and singer, best known for performing “Old Man River” (which was written with him in mind). He played Othello and The Emperor Jones on Broadway. Before he went into acting, he was an all-America football player at Rutgers, played professionally, and was considered one of the best of his era.
IIRC, he also played George Pappadopoulos, AKA Webster’s dad.
Mark Harmon was a pretty good quarterback for UCLA before becoming an actor.
Chuck never seemed very funny to me, but he supposedly commented on David Carradine’s kung fu “His kung fu’s about as good as my acting.” That’s a lot more self aware about his acting skills than I would have given Chuck credit for being.
Let’s see, since Jack Johnson was a boxing pro in (around) 1910, I think that leaves out Shaq, Rodman, Kareem, and Wilt The Stilt.
I guess the only one left is the only one I’ve never heard of: Victor MacLaglen.
Or did I get the wrong Jack Johnson? Not trying to be clever, but I’m not the #1 authority on boxing, here.
Nope, right Jack Johnson: the Best Actor Oscar winning Victor McLaglan, whose name I managed to misspell, seems to have had a somewhat varied career: as well as being a gold prospector, professional boxer and star of numerous John Ford movies {The Informer, Rio Grande, Fort Apache, She Wore A Yellow Ribbon, The Quiet Man}, he was also Provost-Marshal of post WW1 Baghdad {!} And he was in Rawhide. They don’t make CV’s like that any more.
Bruce Bennett from “The Treasue of the Sierra Madre” and many other films won a silver medal in shot put in the 1928 Olympics under his real name Herman Brix.
According to the IMDB, he turns 100 in May.
Greg Louganis went from Olympic diving to acting.
Former heavyweight boxing champ Max Baer had a long string of character roles, as a big strong dumb guy, before creating Max Baer Jr., “Jethro Bodine”.
Merlin Olsen was one of the Los Angeles Rams “Fearsome Foursome” defensive line, alongside Roosevelt Grier and Deacon Jones, before his “Father Murphy” days. Grier and Jones had strings of bit roles themselves, but Lamar Lundy did not.
Johnny Bench was a prison guard in a “Mission: Impossible” episode.
And there’s basketballer Rick Fox, who was quite happy to join the LA Lakers after being dumped by the Boston Celtics, as being in LA helped him get his recurring role in “Oz” and a steady stream of minor roles in other productions.
Chuck Connors got his break in show biz when an agent saw him playing for a minor-league baseball team in, you guessed it, LA. It’s almost heartbreaking how many acting careers have been stillborn because the athlete played in another city.