When Star Trek: The Next Generation premiered in 1987, audiences were introduced to the very first female security chief, Lt. Natasha "Tasha" Yar. She was athletic, tough, commanding, and unafraid to show her vulnerable side, proving that it didn't have to take away from her strength.
Tasha's back story was
brutal: her parents were killed when she was a child, and she and her sister were left on her own on a violent colony, where they dodged rape gangs as they scavenged for food. She escaped at fifteen, and joined Starfleet, where she found the moral center she'd been looking for. She went into security because it was the opposite of the lawlessness she'd grown up with. She remained somewhat haunted by her past, but she led her security team with courage and expert tactical knowledge, and Picard, who had specifically recruited her, trusted her implicitly.
Tasha was killed, senselessly, but returned later in "Yesterday's Enterprise," where she volunteered to go back into the past and fight a doomed battle because she wanted to give her death the meaning it never had. Brave to the end.