According to Variety, Sam Worthington (Hart's War, MacBeth), having
just completed his role in James Cameron's upcoming Sci Fi movie
Avatar, was recommended by Cameron to McG, Terminator 4's director, for
a staring role.
In Terminator 4, Worthington will be playing Marcus, who it's reported
will be a main character over the upcoming Terminator trilogy.
The nature of Marcus' role in "Terminator: Salvation" is anyone's
guess. Terminator 4 will be set post machine/nuclear apocalypse with
John Connor, played by the ever interesting Christian Bale, leading the
good fight. However, given that rumors have Connor being more the
leader-messiah than the main character of the series, perhaps the
various headlines of "Worthington to star in Terminator" are on to
something.
http://www.variety.com/article/VR1117980831.html?categoryid=13&cs=1&nid=2562http://imdb.com/name/nm0941777/