Natasi Daala is a human Imperial admiral introduced by Kevin J. Anderson in Jedi Search (Bantam Spectra, 1994), the first volume of the Jedi Academy trilogy. She is a Star Wars Legends character, and one of the most divisive the Bantam era produced.
The Maw
Daala commands the Maw Installation, a secret Imperial weapons laboratory hidden inside a cluster of black holes, along with four Star Destroyers. Because the Maw is sealed off, she spends more than a decade unaware that the Emperor is dead, the Death Star is gone, and the war has been lost — a premise that does a lot of quiet work, because it lets Anderson write an Imperial commander whose beliefs have never once been tested against events.
The Tarkin connection
Her career is tied to Grand Moff Tarkin, who promoted her and installed her at the Maw. The Legends material is explicit that this was patronage in an institution that otherwise had no route for a woman to reach flag rank, and equally explicit that she was good at the job. Reading her as either purely a protégée or purely a self-made commander misses what the books are doing.
The guerrilla campaign
Once she learns the Empire has collapsed, she takes her Star Destroyers out of the Maw and conducts a campaign of raids against undefended New Republic worlds — the sequence Wikipedia summarises as using "her fleet of Star Destroyers to conduct guerrilla warfare on peaceful planets." She loses, repeatedly and expensively, and after her final defeat she hands command of the Imperial Remnant to Gilad Pellaeon, which is the single most consequential thing she ever does.
Chief of State
The most extraordinary turn comes decades later. In the Legacy of the Force era she is installed as Chief of State of the Galactic Federation of Free Alliances — the successor to the New Republic — and holds the office into the Fate of the Jedi series (Del Rey, 2009–2012). An Imperial admiral ends up running the galaxy's democratic government, and governs it, unsurprisingly, like an admiral. Her collision with the Jedi Order is the spine of the first half of that nine-book series.
The argument about her
Daala is the character Legends readers fight about. One camp reads her as a genuinely interesting study of a competent officer formed entirely by an authoritarian institution, who cannot conceive of any other way to hold power. The other reads her as an antagonist repeatedly written to lose, whose late promotion to head of state was a way of keeping a marketable name in play. Both readings are supportable from the texts, which is a more interesting outcome than most Expanded Universe villains manage.
Where to read her
The Jedi Academy trilogy for the origin — it is pulpy, fast, and very much of 1994. Fate of the Jedi for the late-career political material, which is slower, considerably better written, and assumes you have already done the reading.