dirk, vriska, and equius are the three most important characters in Homestuck because they represent the three pivotal themes that ring true throughout the entire narrative

dirk: arguing with and conflict over alternate personalities, self loathing and crisis over your own identity and clones

vriska: moral ambiguity, the repercussions of abuse and the flow and cycles of said abuse, tainted heroism, ambition, and your status as a villain or hero 

equius: horse