I've on occasion been asked "what made you decide to have a woman as your main action character?", or something to that effect. Honestly, I don't really work that way. I don't sit down and say "Hey, I should write a story with a character that is X". I think of some neat story idea, and the characters I create are the ones that fit the story.
That said, I suppose the fact is that it would never have occurred to me NOT to have at least some of my stories with truly kickass heroines. Looking over my books published thus far (and currently in the pipeline), about the only one that didn't have a pretty badass woman as a major, if not lead, character was my first novel, Digital Knight, and even there, the apparently-fluffy new-age Sylvia Stake manages to lay out a werewolf with a kick to the nether regions (silver-toed boots), helps her new husband face down the origin of the Medusa legend, and single-handedly breaks out of an entire household of demonic entities that were planning on holding her hostage, and instead end up dead at the hands of their would-be prisoner.
In my collaborations with Eric Flint, we had Jodi from Diamonds Are Forever who fights right alongside her fiancee Clint and faces down a monstrous rock-creature with nothing but an operatic-level voice, and Madeline Fathom, delicate-looking blonde secret agent in the Boundary series who is beyond doubt the most formidable person encountered in all three books.
My other solo works – Grand Central Arena and Phoenix Rising – have as front-and-center truly badass women. Grand Central Arena's primary mover is Captain Ariane Austin, once just a daredevil racing pilot, now by default the leader of the small group of humans trapped in the Arena, who has to find a way to lead her people home – and in the end has to face a nearly invincible opponent in personal, one-on-one combat for the chance. She may not be the most physically formidable of the people we meet – that would probably be her mysterious right-hand man, Marc C. DuQuesne, and in the sequel Spheres of Influence we would have to add the Hyperion Monkey King, Sun Wu Kung – but she is the one on whom all success rests.
Phoenix Rising centers around Kyri Victoria Vantage, who is chosen by her god Myrionar as its last hope to revive its religion and save its people. In her quest for justice and vengeance against those who killed her parents and her brother, Kyri – and eventually two companions, Tobimar Silverun (Seventh of Seven, exiled Prince of Skysand) and Poplock Duckweed (intelligent Toad with a knack for poking his nose where it doesn't belong) – end up facing the driving forces behind a conspiracy that spans their entire continent.
To me, it wasn't a choice to make these characters female. They simply were.
That probably comes from my reading as a child. While I certainly hold in high esteem many pieces of writing that are wholly or to a great extent dominated by male heroic figures (such as the works of E.E. "Doc" Smith, Asimov, Niven, etc.), some of my earliest favorites were filled with female heroes. The Oz books by L. Frank Baum, for example, were dominated by girl heroes – Dorothy, Trot, Betsy, Polychrome, Ozma – and even the less-frequent male heroes were either accompanied by a female, or often needed help from (sometimes more sensible) females such as Glinda the Good. Dorothy walked through perils and overcame her fears with a wide-eyed, invincible innocence, kindness, and determination that did not allow for the possibility of failure. The young boy Pip survives multiple harrowing adventures to discover that he really isn't "he" at all, but the shapechanged form of Ozma, the true ruler of Oz. Trot and her friend and companion Cap'n Bill survive everything from a maelstrom to being lost underground to being shrunk to the size of a berry and confronting a true Wicked Witch, always with Trot's calm faith supporting her and those around her.
The "Little House" books, based on the actual life of the author Laura Ingalls Wilder, emphasized these things to me; here was a real little girl who might have lived a hundred and more years ago, but was just like me, or the me I'd like to be, in many ways – curious, sometimes getting herself into trouble, courageous, willing to handle hardship for the sake of her family, and sometimes willing to strike out at those who hurt her, because it had to be done.
Later reading that I chose just reinforced my basic assumptions that – when it came to heroism – there was no difference at all between boys and girls. The Danny Dunn series had Irene Miller, the perfect balance between the irrepressible Danny and the gloomy Joe – a girl as physically capable as either boy, and possibly even smarter than Danny, the putative main character. Nancy Drew and her friends were always able to crack the case, even when the adults around them didn't see the solution. Alice didn't need anyone's help in Wonderland.
` One of my favorite science fiction authors – and one who, indirectly, led to my own publication – was James Schmitz. Schmitz' most famous work is probably The Witches of Karres, which features the titular Witches in strong secondary positions, but the work of Schmitz' that influenced me most was the Telzey Amberdon series, featuring a teenage girl who suddenly develops powerful psionic abilities which plunge her into multiple potentially deadly adventures.
Schmitz also gave me The Demon Breed (AKA The Tuvela) in which a smart scientist manages to, quite literally, terrorize an entire group of alien invaders until they flee, convinced that she is some sort of superhuman monster, and the Trigger Argee series, whose young heroine has no special powers but still manages to perform as capably as any space-opera hero.
Some iconic images in other media tended to stick with me, too: Jaime Sommers, the Bionic Woman, former tennis-pro turned teacher and sometime secret agent, who was more than capable of handling top-secret missions all by herself with no man to do the handholding; Ellen Ripley, terrified by her first encounter with alien monsters and instead of turning away from it, transforming herself into what may be one of the most iconic badass figures in all modern cinema; Velma from Scooby-Doo, always smarter than everyone else around her and the one who cracked every case in the end.
I also was a roleplaying gamer since the late 1970s, and one of my earliest influences there was a gamer named Steve Reed. Steve played female characters more often than male characters, and did so with such absolute nonchalance and normality that it never seemed "odd" to me, though it apparently did to some other people. I ended up playing almost a perfect split – something like 48% male, 48% female, and the remaining 4% things for which the sex wasn't terribly relevant (an intelligent toad in a group of humanoids, a shapeshifting blob, an automaton).
So when it came to writing, it honestly rarely occurs to me that I'm writing "a woman" as a character. I'm writing a person, who may be male or female. The main characters will naturally kick ass – it's their job! And thus some of them will, and must, be women. They're half the human world, they've got as much reason to defend it as the men do. And defend it they will, matching the others stride for stride, strike for strike, strength for strength.