Elizabeth "Betty" Gray is the life-long love interest of Mark. According to their origin story, they first met during their late childhood or early teen years. Betty had wandered away from her parents' farmhouse and got attacked by wolves. Mark answered her cries for help and fought the hungry animals by himself. A grateful Betty tended to his wounds and introduced him to her parents. She later sewed for him Mark's trademark shirt.
A couple of years later, Mark attempted to visit Betty again. He found the farmhouse burnt to the ground, apparently destroyed in a raid by Native Americans. He mourned for the apparently deceased Betty. Actually, her parents were dead but Betty had survived. She was living with relatives in a small town. Mark discovered her tracks later, while Betty was held prisoner of a relatively high-ranking British officer. Her family was suspected of ties to the American revolutionaries.
Mark's attempt to free her carved his reputation as a revolutionary and directly led to the founding of the Wolves of Ontario organization. She is the only female member of the group and tends to end up with the less glamorous chores in Fort Ontario: feeding the perpetually hungry "Wolves" , tending to their wounds and overseeing the supply stocks. This has not stopped her from getting actively involved in numerous missions. Occasionally because of getting specifically targeted by opponents. Other times because of insisting of following Mark, regardless of his wishes or outright orders.
A frequent plot point in stories is Betty tending to be jealous and fiercely possessive of Mark. The hero does have wandering eyes and hands. He is often caught flirting with, kissing or embracing other women. The rival love interests are mostly one-shot characters. An enraged Betty tends to attack Mark with a variety of objects or her sharp fingernails. Some of the female villains receive the same treatment and, on occasion, Betty draws blood. Attempts by Mark to organize "secret" missions, have Betty going on tirades about his secret meetings with brunettes, blonds and redheads. She tends to follow her lover, in order to keep an eye on him.
A less often plot point is Betty's tendency to attract villains. Which occasionally comes in handy, particularly in "cloak and dagger" storylines. A number of stories have her infiltrating the houses or organizations of various villains, playing their ideal love interest. Whether that is a refined aristocrat or a childish damsels in distress, Betty seems to have enough theatrical skills to play the part. Becoming a useful mole among their ranks.
A third source of plots is her family connections. The Gray family seems to have been involved in past adventures involving witchcraft, hidden treasures, coded maps, etc. People involved in ages-old treasure hunts tends to track Betty and attempt to drill her on information concerning the object of their obsession. On the other hand, Betty's visits to surviving relatives seem to invariably result in meeting ruthless villains.