My fave Trek character has never appeared on screen. His name is Taran'Atar, and his face strikes fear into the hearts of all he meets, for he is Jem'Hadar.
he's a new character introduced in the DS9 novels that are set after the DS9 series finale.
After Odo returned to the Great Link, he took a page from his peoples' dispatching the Hundred (to learn about the galaxy before returning to bring that knowledge to the Link), and gathered a team of Jem'Hadar to go back to the Alpha Quadrant and learn how to live as free beings.
There was a . . . complication during the mission, and only one Jem'Hadar survived to reach DS9 and place himself under Col. Kira's personal command.
Just one problem; the Jem'Hadar don't want freedom. They serve the Dominion. They have always served the Dominion, and always will serve the Dominion. It is The Order of Things.
Nonetheless, Taran'Atar remains (because it is what the Founder "Odo" commanded). He can't understand the purpose of his mission here, but understanding is not his goal. He will simply obey.
I've always had a thing for the truly alien characters of Star Trek. The Borg, the Cardassians, the hirogen, the Vulcans, the Founders, and the Jem'Hadar.
Naturally, the Dominion War ended just months before his arrival, and many of its wounds were still fresh. There's no one on DS9 who hasn't lost a loved one to Jem'Hadar shock troopers. "Chief" Nog especially blames them for the loss of his leg.
Taran'Atar is a killing machine. His current mission does not call for anyone's death. Should that change, however, he is more than capable of slaughtering every living thing on that station. The Jem'Hadar were not bred for compassion.
I especially like how Taran'Atar sees "normal" life aboard DS9 as being completely alien. These people are not warriors. They are undisciplined, physically weak, driven by their emotions, and working at cross-purposes with no clear sense of Order. Even the so-called "Prophets" of the Bajorans do nothing to intervene.
He was deeply shocked to see how weak and helpless non-Jem'Hadar children were. He was equally surprised to learn that, unlike the adults, the children do not fear him. . .
They haven't learned to.
"The Beasts know much that we do not." -Ancient Jedi proverb