Jackie first took note of the American prodigy Hunter Rose, when he was still known as Eddie, at the world fencing championship in England. She was a coach on the British team, and was struck by Eddie's style, speed, and finesse. She brazenly approached him when he was in the locker room and asked him to leave with her. Despite being over twice his age (he was fourteen and she was thirty-six), she was stunningly beautiful, and he was enthralled by something in this world for the first time in his life. Jackie's illicit romance with Eddie continued; she took on the role of a mentor as much as a lover. He was bored with fencing with everyone else, but thrilled to do it with her. She taught Eddie to search for, and love, the game within life.
No one knew that Hunter was with her, and he was listed as missing, but eventually the authorities gave up the search.
Jackie eventually died. She was terminally ill since before ever meeting Eddie. She never mentioned her illness, nor did she display any obvious signs. She had prepared herself for it for quite some time, but decided to continue living and playing the game despite being sick. When her death came, it came quickly, and came as a shock to young Eddie. He would come to discover that she knew she was sick, and had set her affairs in order around a year before her death. Her influence on Eddie would be especially obvious after her death. They had playfully drawn faces on their fencing masks when she was live. After she died, he designed a new face on his fencing helmet--the black and white visage of the now-classic Grendel mask. He now felt free of all connections and morals, free to treat life as a game. Upon traveling back to America, Eddie took the name Hunter Rose and began his new life. He wrote his first novel within a month, and murdered his first man the month after that.
It's unclear whether her real name is actually Jocasta Rose. Christine Spar tries to track her down but can't find anyone by that name, and suggests that it is a pseudonym of Hunter's invention. However, she does call herself Jocasta Rose in multiple comics appearances. It is possible that she invented the name herself.