In Homestuck, trolls were an alien race whose interaction with the human characters became one of the main focuses of the story. Originally introduced as antagonists who (as their name suggests) "trolled" the characters over the internet, they were slowly introduced as more prominent characters, and, a year after Homestuck started, the backstory of their race and culture was shared, which was fascinating to fans.
Biologically, the troll race has some major differences with humans. Despite outward similarities of appearance, the trolls are insectoid and nocturnal, and are hatched from eggs laid by the mother grub, a gigantic insect that lives in their planets breeding caverns. Like many insects, most of the larvae (called "wigglers") perish quickly unless they find an animal-like guardian (called a "lusus") to protect them. The culture of the trolls is brutal and callous, with the weak offspring being killed either by chance or by their government. Because of this, the surviving trolls are super-strong with great endurance. The story shows them, for example, being able to continue functioning even after being impaled or having a limb removed. They also have a system of blood caste, with different types of blood pigmentation ranging from red to purple, with the color of a troll's blood reflecting their lifespan and social status. The social status of blood caste is ruthlessly and violently enforced. Despite of, or perhaps because of, the troll's brutal and racist society, the trolls that survive to adolescent form strong social bonds. Their social and interpersonal relationships have more dimensions than humans, since procreation (apparently) involves finding two partners, one marked by romantic love and the other requiring something that can best be described as "romantic hatred", and with friendship and mediation both being seen as a type of romantic emotion. Also, since they lack direct biological parents, and all trolls in a generation are siblings, they lack any concept of incest, and find the human prohibition against it strange. Also, since they display gender only as an aesthetic, and pick sexual partners without regard to gender, they have no concepts of homosexuality or heterosexuality, and also find it strange that humans even have words for the concepts.
(The fact that trolls have four quadrants of romance has much to do with their popularity among Homestuck's teenage fanbase: the possibilities of shipping all the different characters in all the different combinations is one of the main attractions oh Homestuck, for many fans.
These basic facts about the biology and social dynamics of an alien species were described, both indirectly and directly, across several hundred pages of the webcomic, which took several years in real time. So these basic facts, and the later realizations made from them, were revealed in a roundabout fashion, and slowly became part of the comics larger narrative.
What is interesting to me is that despite most of the focus on Homestuck being on its multimedia and "meta" nature, in several places, it is a science-fiction story. Although they are presented at times in a humorous or odd fashion, the trolls are actually designed with a coherent idea of an alien race with a different biology, and then expands on how differences in reproduction and lifecycle could effect the psychology of an entire society. In this way, the alien trolls in Homestuck are more realistic than, say, the array of humans with rubber foreheads on Star Trek