I Haven't seen 42 yet but I have seen the ads as well as the trailer and some promotional interviews. Ralph Branca has been featured in the interviews and appears to have a prominent role in the film.
Ralph Branca is one of the Brooklyn Dodgers that befriended Jackie Robinson rather than shunning the new player. According to wikipedia Branca stood with Jackie Robinson for Opening Day lineups in 1947, when other Dodgers refused. Nothing quite like being on the right side of history.
Branca is also known for giving up "The Shot Heard Round the World" to Bobby Thomson in 1951. The Home Run by Thomson completed a victory for the Giants in a 3 game series to determine the NL champ.
The three time all-stars career was much bigger than that single game. He pitched for a dozen years almost entirely with the Dodgers - He pitched in two World Series (1947, 1949).
Jackie Robinson's first season (1947) was Branca's best as he posted a 21-12 record with 4 shutouts and loggged 280 innings. The 21 Ws and his 147 Ks were both good enough for 2nd in the league while his 2.67 ERA was 3rd.
Ralph Branca is still alive at age 87 and can be seen promoting the film 42 on several baseball and sports outlets. There is also an official Ralph Branca website for fan who are interested in autographs and other memorabilia.
For the Collector
I picked up the above Branca card for $1 at a show last April. The card may be a little rough, but any vintage Brooklyn Dodger card for a buck is like stealing. The Lo E-Bay for a really rough 51 Bowman Branca among recent closes is $3.78, for $4.04 you could get a much nicer card. The card peaks at $69 for a PSA 7 NM.
1949 Bowman #194
The Bowman RC of Ralph Branca started at $66. High numbers for the 1949 Bowman set start at #145 - Hall of Famers and Stars like Branca are virtually impossible to find. Best of luck to anyone looking to build that baby. The card peaks at $109 (BVG 7.5 NM+)
The only Topps card for Ralph Branca is from the iconic 1952 set #274. The low recent auction for an acceptable condition card was $11.94. A PSA 8 NM-MT went for a tidy $414. If your willing to settle for PSA 5 EX you can get the card at the far lower price of $95. It should be noted that the card is part of the middle series of 1952 Topps which runs #251-310. I have found commons in this series run 2-3x higher then the low series, stars and HoF vary but typically multiply more.