Saint Stephen is the patron saint of deacons. Here he is pictured with his attributes of the stones used for his martyrdom and a book. Is he wearing a dalmatic? I think so. Perhaps those deacons who are reading this will be able to tell.
One of the features of Christian iconography that I find fascinating is the convention of portraying saints with the implements of their martyrdom. Saint Stephen as he is pictured here is serene, yet he died a terrible death and that death is remembered. Indeed, his life cannot be recalled, or his future glory celebrated, without reference to his death.
In this way, the image of a saint becomes a witness not merely to virtue or good works, but to the paschal mystery, for the saint has passed through suffering and death to life.