Each player in Sburb has a mythological role which consists of two components: a class and an aspect. A title can be assembled from any combination of class and aspect: John is the Heir (class) of Breath (aspect), while Tavros shares his aspect as the Page (class) of Breath (aspect) and Equius shares his class as the Heir (class) of Void (aspect).
Aspects are a form of generalized "elements", in that they are primal forces of reality. Classes describe mechanics and intended roles, "channeling" the aspect into possible action and powers. Classes come in active (-) and passive (+) pairs, which can mean multiple things but roughly described as the active classes employing or affecting their aspect directly and for his own gain, and the passive classes being affected by his or her aspect, and sharing his or her actions with the team.
Do note though that literal interpretation of the aspects' and classes' names is misleading, i.e. "Prince" actually means "destroyer", and "Light" means "fortune".
Heroes with different aspects can end up with very similar powers depending on their class. The Life and Doom aspects may be radically different, but depending on the class their powers may end up being similar.
Player abilities may also manifest in ways contrary to their aspect if they are heavily resistant to their true calling, or if an outside influence corrupts them. This happened to Rose Lalonde, and may have also occurred to other players in the troll session (as their entire society was corrupted by Doc Scratch and Lrd English).
The terms "Hero" or "Player" can be used in lieu of the class when the speaker wishes to be generic, i.e.: John and Tavros are "Heroes of Breath" and Roxy is "a Void player." Both components of the title appear to have some mechanical effect on the game, depending on the class or element assigned. The salamanders of the Land of Crypts and Helium and the B2 Carapacians use the term "Noble" to refer to their Heroes, possibly implying that Nobles suffer and become martyrs, rather than saving others as a Hero might.
Sburb may design planets with the titles in mind. For the kids one part seems to come from their aspect, while the other comes from their associated element, or a force actively opposing it (dark clouds in John's case and frost in Jade's). The trolls' planets mostly relate to their interests, but some show a clear connection to their titles.
Doc Scratch implies that every session will have a Hero of Time, and if the breeding duties are indeed linked to the Hero of Space they would be a constant in the game. Calliope has confirmed that these two aspects are indeed the minimum requirement for every session. The only exception seen is with the post-Scratch kids, who lack both Time and Space players, and as a result lack a frog planet, though this is likely a cosmic consequence of the eventual arrival of the pre-Scratch players, with all their planets in tow, into the post-Scratch session.
There are at least two rare classes referred to as "master classes". One, the Muse, is "the most passive class" and strictly for females. Its counterpart, Lord, is the male master class and the most active class.
It is entirely possible that the number of players in a given session will determine what titles the game can and will assign. It appears games with four or more eliminates the chance to receive master classes, which may serve the purpose of fulfilling multiple roles in under-populated games.
"[...] one who destroys heart/soul, or caUses destrUction throUgh heart/soul [...]"
Simultaneously conscious as both real and dream selves, with additional personalities as the Auto Responder and within Jake's dreamscape after Jake has woken
In one of Karkat's memos, Kanaya speculates that Skaia assigns titles to players to challenge them, rather than to suit their strengths.
This would certainly explain some of the apparent inversions, such as Rose being the Seer of Light despite her fascination with darkness and horror, and Jade's title as the Witch of Space despite her life never leaving her small island. However, this theory should be taken with a grain of salt, considering that the titles of a lot of the players match them perfectly.
It could be speculated that players are meant to "grow into" their roles; that is, when they first begin the session their title and its duties force them outside their comfort zone and seem very unsuited, but a fully realized Hero has matured into the role the game has assigned them.
It is hinted that Calliope's power as the Muse of Space may be the power to physically influence all that she imagines in the form of fanfics and artwork.
Hussie does indeed have a Hero of Space outfit, but he has stated that it was just a cosplay, and while many fans had been calling the god tier Waste of Space, the class name was never actually revealed.
Discounting the trollsprites, when B1 kids and the remaining A2 trolls arrive in the B2 session, the session will have one Hero for almost all the aspects, with the exception of Space and Doom, with Space having two (Jade and Kanaya) and Doom having none.
It could be that the title of Lrd English is related to Caliborn's Echeladder, as it bears a similitude with John's final non-God Tier rung, Heir Transparent.
Fitting the common theme of playing cards in Homestuck, a player's aspect could be analogous to a card's suit, and his or her class could be analagous to its rank, based on the format of cards' names and players' titles. (ex: Prince of Heart, Jack of Hearts).