Niobe is a human from Zion, being one of the rebels participating in the war against the Machines and the Matrix. She is the captain and pilot of a Zion hovercraft, the Logos, the smallest (and therefore most maneuverable) ship in the human fleet with a crew of only three: herself, weapons expert and First Mate Ghost, and Operator Sparks.
Within the virtual world of the Matrix, Niobe is one of Zion's most gifted martial artists. She has "killed" at least one Agent, survived multiple encounters with the Merovingian's superhuman thugs, faced Seraph in one-on-one combat, and even managed to survive and escape from a confrontation with the replicating entity Smith.
In the real world, she is the most skilled pilot among the rebel forces. She demonstrates this on several occasions. In one scene during The Matrix Revolutions, she maneuvered the rather massive hovercraft Hammer through the narrow, cluttered passage of a mechanical line (while under heavy attack and pursuit by Sentinels), a feat no other pilot has successfully performed. She also performs a 270-degree flip with the hovercraft, as an evasive maneuver, which apparently no previous pilot had even attempted before. She also gave up her ship to Neo so he could go and stop the machines. When questioned about this since she didn't believe in the prophecy, she responded she still didn't, but she did believe in Neo.
Niobe was once romantically involved with Morpheus, but their relationship broke apart after Morpheus received his revelations from the Oracle and started to preach the prophecy of the One (a prophecy Niobe has never truly believed in). After breaking up with Morpheus, Niobe eventually becomes involved with Commander Jason Locke, a taciturn, practical man who is in many ways the exact opposite of Morpheus. Both Persephone and The Oracle insinuate that Niobe is still in love with Morpheus when they confront her in Enter the Matrix.
At the end of The Matrix Revolutions, as the retreating Machine army obliged the new peace bartered by Neo, Niobe is seen embracing Morpheus, perhaps an indication of a renewal of their romance. (One reference in the Special Features also intimates that they have gotten back together.)
Niobe has gone on to play a major role in The Matrix Online, acting as one of the "leaders" of the obviously enlarged Zion military since Locke, being free-born, cannot jack-in. After the Logos was taken by Neo and crashed in the Machine City, Zion was able to build her a new ship, named the Logos II. When the Imposter Agents appeared, she made a speech to the Zionite redpills in the ensuing race for Neo's digital remains, which had been blown into fragments. She claimed that Zion's progress was pathetic and they had to step up their efforts. Before the General made an alliance with Niobe, Niobe was busy avenging Morpheus's death by trying to find more information about the Assassin. She eventually got into a battle with a last remaining copy of the Assassin post-Death of a Destroyer and was wounded, but was saved by an unknown redpill.
In Chapter 5.1 of The Matrix Online, Niobe had a meeting with fellow Zion operatives inside Bishop Imports in the International District to test out a set of chemicals that were upgrades meant for the Agent programs. After consuming the chemicals, Anome, her trusted subordinate, shoots Niobe and all Zion operatives in the meeting while an operator of his hovercraft pulls the plug on one of his surviving crewmembers who isn't in on his plot. Niobe's floor is sealed and there is no way to access her floor with both the elevator and staircase systems. During the recent set of critical missions, Ghost and redpill operatives from all parties are currently attempting to save her.
In Chapter 5.2 of The Matrix Online, Niobe was rescued chronologically after the fourth Zion critical mission. On the Recursion instance, Ghost leads a rescue team to Bishop Imports in Ueno, while the Effectuator (a program hired by the Merovingian who controls his constructs), and other redpills protect the hardline systems to facilitate the operation.
Other minor roles include briefing and de-briefing Zion operatives during missions, and rewarding Redpills with special items.