How did Saruman know who Gimli was ?

[Inziladun]

Originally Posted by CSteefel

Only one I can think of is Wormtongue, who would presumably have heard the name from Eomer or one of his men, since this is where Gimli announces that he is Gloin's son. Since Eomer lent them the horses, and the guards at the gates of Edoras knew that they were returning with those horses (as Gandalf notes upon arrival), the names of the three wanderers who they had met to the north would be known to Wormtongue...

Now that I think about it, that's probably the most likely. Éomer did indeed hear Gimli say he was the son of Glóin at their first meeting, and that was the only time Gimli's father is mentioned in that part of the book. At the time Aragorn, Legolas, and Gimli see the old man at the edge of the trees, only Gimli's name had been said when the old man was likely to have been watching.