St. Margaret of Antioch, also known as St. Margaret the Virgin and St. Margaret the Martyr, is purported to have lived at the end of the 3rd century during the great persecution of Christians under the reign of Emperor Diocletian. Disowned for converting to Christianity, Margaret moved to the countryside where she attracted the unwanted attention of a man who demanded she both marry him and disavow Christianity.
The teenage Margaret, already pledged to a life of chastity, refused, at which point she was threatened with all sorts of tortures from which she was miraculously delivered. Satan tempted her in her cell but was rebuked, only to return in the form of a dragon and swallow her. The strength of her faith (or the cross she carried, depending on story) caused the dragon’s belly to burst open and allow her escape.
For this reason, Margaret is commonly depicted with a dragon. Also for this reason, Margaret is (rather disturbingly) the patron saint of childbirth.
As an Aside: When Margaret was finally beheaded, she is said to have prayed for babies to be safely delivered just as God safely delivered her from the dragon. Still, seriously, ripped opened the dragon’s belly.
Renaissance and Later Images
Images of the last 500 years (renaissance and later) tend to downplay the violence of the scene.
Medieval Images
From the above images, you might think Margaret just happened across a dragon one day, at which point she either slew it, subjugated it, or took it home like a lost puppy. Medieval images (even some very late medieval) leave no such ambiguity.
As an aside: How do I determine what is renaissance and what is medieval, especially since some images in both group come from the late 15th century? The 14th and 15th centuries are sometimes called the Late Middle Ages: northern culture was still medieval while southern culture has embraced Renaissance ideas. These ideas include standards of artwork. The visual realism of the first set of images is Renaissance. The styles of the second group are medieval, although they are becoming increasingly renaissance-ish.
Veneration
Pope Gelasius expressed serious suspicion of her existence in 494. However, she actually became more popular in the High Middle Ages, and she remained on the calendar of celebrations until the most recent major edit of the calendar, which happened in 1969.
Removal from the calendar does not overtly state the saint does not exist. It does recognize the lack of significant evidence, however. In the case of Margaret, her acts are considered “entirely fabulous.” St. Valentine is the most well known saint to be removed during the 1969 edit.