I agree that it was Cyndane (who probably calls him al'Thor to try to distance herself from her ideas of Lews Therin), but my impression was that they were sending him on a suicide mission to distract Rand from something else. I'm not committed enough to what you know I believe to be a very second-rate series of books to comb through and read all the Dark Prophecy and such, but what I remember was that either you turn Rand to the Shadow, or you maneuver him into a place where he does more damage to his friends than to his enemies, or you kill him on the slopes of Shayol Ghul at the Last Battle. The Forsaken don't expect Isam to survive, but he'll distract Rand in a major way while they do something they really, really have to do (like steal Callandor or something).

Also, although the books are aesthetically a train wreck, the Isam section showed how much better the books could have been if we had seen more motivations for the evil characters earlier on. The later books have had some interesting moments like the Isam POV and the point where Ishamael/Moridin says he's tired and wants to break the cycle for that reason. Other than that, evil has just been pathetic, or a caricature, or both.