Apollonius's characters are complex; the two main sides of Medea's character—impressionable virgin and dangerous sorceress—can be seen as confusing if viewed from the perspective of that “consistency” which Aristotle prescribed for dramatic character. Apollonius is rather interested in the similarities and differences between the power of love, the power of persuasion, and the power of drugs, and this interest is explored through the presentation of Medea, whose character is thus a function of the narrative. Jason's character, on the other hand, brings persuasion and stratagem to the fore; see especially his testing (peira) of the crew after the passing of the Clashing Rocks (2.607–649), and the praise of muthos and mētis at 3.182–193. His story is of the familiar type of rite of passage (cf. Orestes, Theseus, etc.) in which a young man must accomplish a dangerous set of tasks before assuming his rightful position (in this case a kingship which had been usurped by Pelias); that Jason seems often overwhelmed (amēchanos) by the enormity of what he must do and finally accomplishes it only through Medea's help finds many parallels in related stories, but also marks the difference between his exotic story and that of the Homeric heroes. The characters of both Jason and Medea are examined in greater detail in two linked essays.
Some recent writing on characterisation in the Argonautica is previewed here.