Ronde Macura is one of the eyes and ears for the Yellow Ajah. She discovered forkroot, which prevents a channeler from being able to touch the One Power. She doses Nynaeve and Elayne with forkroot and tries to send them back to the White Tower, as they were considered runaways. They were rescued by Thom and Juilin, though. Later, Macura was recruited by Tuon to produce forkroot.
For more details on Ronde Macura, visit Encyclopaedia WoT.