Star Trek: Enterprise
In the third season premiere of Enterprise, the Xindi arc officially kicks off. Technically it began with the second season finale, "The Expanse," in which the horrific terrorist attack on Earth occurs and Archer is asked to undertake the dangerous mission to thwart, if possible, any follow-up.
At the time, I read a bad review of this episode because it seemed like Star Trek, instead of seizing the opportunity to do something bold and new (relatively speaking, for a season billed as one complete arc; although Deep Space Nine more or less featured the Dominion War throughout its final two seasons, there were many episodes therein that did not feature material related to the conflict) the show felt like it was going in a ho-hum direction as Archer and Trip negotiate with an alien who doesn't feel significant enough for such an important occasion.
(Yeah; by this point it was painfully clear that everyone was ready to give Star Trek a good, long rest, if there was going to be a grand revival at all. Fortunately there turned out to be one.)
But here we are all the same, and by the time we get our first look at the Xindi, in the episode called "The Xindi," we do in fact dive directly in, meeting the ruling Council, all the key players including the scientist Degra, later to be heavily featured (especially in one of the season's best, "Stratagem"). And by the way, we see these guys first and last thing this episode, and at this point they're nowhere near interacting with Archer directly. Which does happen to be a bold departure for Star Trek.
These are the five Xindi species: the Reptilians (lead villains), Insectoids (back-up villains), Arboreals (first of the sympathetic ones), Primates (Degra is one of these), and Aquatics (along with the Insectoids, one of two completely CGI species within the bunch). There had been six species, but the Avians became extinct in the cataclysmic events that led to the attack on Earth...
The episode also features the debut of the MACOs (Military Assault Command Operation), who are a detachment of soldiers meant to support Archer's mission (presumably limiting the possibility of redshirt syndrome, although some MACO do in fact die during the season). Among the actors playing these guys are Daniel Dae Kim (later to be featured on Lost) and Steven Culp (who at the time was making a career of being the MVP of recurring character actors, being featured in such capacity on The West Wing and, most significantly, JAG).