Vriska

Vriska Serket is one of the main characters from the webcomic Homestuck, first introduced in Act 5 as one of the twelve Alpha trolls. For better or worse, the introduction of the trolls skyrocketed its popularity on Tumblr, and Vriska was one of the most notable Trolls. For whatever reason, she ended up sticking out the most, and became the most notable instance of the sexywoman phenomenon.

Basic Information
This is an abridged version because Homestuck is very complicated. Vriska is introduced as, to quote the comic, a "bluh bluh huge bitch," and that doesn't really change throughout the entirety of the comic's run. She's responsible for several tragedies among the main and side characters, including crimes such as murder (a LOT of murder actually) and possibly being responsible for the main villain. She also is a complicated character with a somewhat tragic backstory, so a lot of people like her for that. Part way through the comic she dies and her ghost goes through a redemption arc, but then the death is undone through time shenanigans and so is that redemption arc (this is Homestuck, this kind of thing happens a lot). We're not discussing the Epilogues and Homestuck^2. "But that's where the profile pic comes fro-" I know and I don't care.

If you want a more in-depth summary, look at her page on the MSPaint Adventures Wiki.

Angst
Her Lusus was a giant spider who fed on trolls, meaning that from a young age she had to learn how to trick and manipulate Trolls so that she could use them to feed her Lusus and avoid getting eaten herself.

Quotable Catchphrase(s)
Any remarks about "all the luck" and "irons in the fire," especially in the earlier days of Homestuck.

Dominating
Literally has mind control powers. Getting less literal, her early relationship with Tavros is more or less just relentlessly bullying him.

Eye Imagery
Has seven pupils in her left eye. Also lost that eye but she got it back through godtiering.

Questionable LGBT Rep
Canonically bisexual, having interest in/having relationships with men and women (Tavros, Eridan, Jegbert, Kanaya, Meenah, and Terezi.), along with it being popular fanon and semi-canon that she is a trans woman. She's also Vriska.

Knifemurder
Canonically recognized as a serial killer of trolls due to the aforementioned "has to feed spidermom" thing. Also has no issue killing characters onscreen, and is responsible for the death of two of her fellow trolls (though one of them came back so it's fine).

Monster Features
Even by troll standards she has weird features, such as her fangs and the aforementioned multi-pupil eye. Going by Friendsim, this isn't actually too uncommon among ceruleanbloods.

Animal Theming
Strongly associated with spiders - it's why she does so many things in eights, has eight pupils, and even has a spider lusus. This, of course, ties in perfectly to her associated Zodiac sign, which is a scorpion.

Power
Beyond the aforementioned mind control, she's also the only one of the Alpha trolls to reach godtier, meaning that she can use her abilities as a Thief of Light to the fullest and steal luck from people. She also can't die unless it's under very specific circumstances.

Theme Song:
Has several in the Homestuck soundtrack but you already know which one I'm going to link don't you.

Villain
She's VRISKA.

Vriska Archetype
Literally the character the archetype was named after.