Medea is a clever women who is able to control her emotions in order to achieve revenge. Through her conversation with Creon when he attempts to banish her, we can clearly see her intellect as she manipulates Creon into letting her stay. Despite her anger, she is able to quickly grasp Croen's love for his daughter and use it as a means to persuade him.
Croen clearly cares a lot about his daughter and fears Medea's cleverness. The reason he gave for Medea is not fear of his own death, but rather the fear that Medea "may injure [his] daughter mortally" (line 283), a fear that is well justified given Medea's reputation as "a clever woman, versed in evil arts" (line 285). He mentions his "daughter and Jason" (line 287), before even mentioning himself when speaking of Medea as a threat. This love for his daughter is what drives him to face Medea and attempt to drive her out.
Medea's cleverness is seen almost like a deadly weapon, more deadly than her anger. Rather than describing her deadly rage, it was her cleverness that she described as something to be "objects of envy and ill-will" (line 296) which will cause her to "become hated" (line 301). The king later on says "a sharp-tempered woman, or for that matter, a man, is easier to deal with than the clever type who holds her tongue" (line 319-321). It is Medea's ability to persuade people by speaking, and indirect means that Croen is afraid of. The king is then manipulated into letting Medea stay when she begins to plead to him by bringing up her children and saying "have pity on them! You have children of your own" (line 346).
It is this 'cleverness' of Medea that makes her such as unique protagonist. Unlike the Odyssey where Odysseus' ways of telling lies and his various disguises are cleverness is celebrated and endorsed by Athena, within Medea's 'cleverness' hides tragedies waiting to unfold.