Thanks to Lyly for alerting me to the first casting tidbit for Season 4, from secretagentman.
Who do you think these two new characters are and who are they related to?
Two new characters begin in eps. 2, possibly extending the rest of the season, and perhaps next season. Russell, a brilliant mathematician in his late 30's and Charlotte, an attractive, athletic academic. Names may change of course.
Source: Secretagentman
Here is some additional info from Ausiello.
Spoiler: Lost Introduces the Other Others!?
Far be it from me to speculate on whether or not the new Lost casting intel that just landed in my lap are for the Other Others whose arrival was imminent in last season's finale. But if you want to wager about who these newbies are, who am I to stop you? Herewith, the evidence. Do with it what (you and I both know) you will.
First up is the recurring character of Russell, described as a brilliant mathematician in his late thirties who is "capable of great insights and has a tremendous knowledge across various scientific fields." Well, won't that be helpful. Unfortunately, he tends to be too direct for his own good, and as a result, his personal relationships don't always add up. Russell is scheduled to turn up in Episode 1.
Also recurring is Charlotte, a hot twentysomething who is said to be "precocious, loquacious and funny... a very successful academic who also knows how to handle herself in the real world." Interestingly, she, too, has a tough time relating to people. Beneath the surface, there's "lots of repressed and pent-up emotions."
Come Episode 2, when Charlotte debuts, who would you like to see play her? And what about math-dude Russell? Post your casting tips below
Source: SpoilerTV