After the 12th issue of Authority Warren Ellis left the title and Mark Millar took over. He did some extra fleshing-out of Jenny's history in the Jenny Sparks: Secret History of the Authority limited series, focused on the origin stories of the members of the Authority. Most of Millar's additions are furthering Ellis's backstory and intermeshing Jenny Sparks with important historical figures of the 20th century, including Albert Einstein, Ernest Hemingway, Adolf Hitler, Jacques Cousteau, John Lennon, Princess Diana, and many others. He also added a number of fictional characters into the mix: at one point, Jenny is seen in a Vienna cafe talking to a lawyer who, it is implied, is Rumpole of the Bailey, while at another, a Nazi officer refers to her "illustrious former boyfriend Dr. Jones", an apparent reference to Indiana Jones.
Jenny is one of the characters Ellis created to protect humanity, present a facet of the coming age and do something specific for it in a given century. Since the thesis given by the Doctor goes that humanity as a whole thinks that a century begins with the centennial year, so the mass unconscious of humanity creates these heroes in the beginning moments of the centennial year. (see also: Century Babies).
Her being "The Spirit of the 20th century" is not only a title. Jenny was the one most tied with the century itself, always being in the centre of things, while her state of mind mirrored the spirit of the particular age. This is best shown in Stormwatch #44, where Ellis takes a ride through the 20th century, telling Jenny's story. This is accentuated by the artwork of Tom Raney, the inks of Randy Elliot and the changing palette of Laura DePuy and Wildstorm FX. The style, the layout and the colors change with each era of Jenny's life mirroring the black and white of film noir, the three colors and simple lines of the Golden Age or the dark, oppressive backgrounds and gritty characters of the eighties.
Jenny Sparks is a pretty, yet foulmouthed, chain-smoking, bisexual blonde who sleeps around. She usually wears white clothing with a Union Flag prominently displayed.
Her long life has made her cynical and aggressive towards everyone. She saw that "heroes" only ever went after the effects and never the causes of the problems in the world. Henry Bendix's promise that his Stormwatch would not act like that brought her into the team. After a long time this finally gave her purpose and allowed her to embrace her vision of a better world. This same vision also inspired her to create the Authority.
