you can wait untill i get the OOC up to decide, this topic is mostly for discussing/adjusting the idea so it appeals.
but for now,
the Eldar were once the dominant race in the galaxy, defeated the Necrons, kept the orks under control and manageable, then they all decided to have one massive orgy for a few thousand years. the psychic impression they created (all eldar having some psychic ability), eventually sparked into sentience, became one of the four Chaos Gods, and annilated their coreworlds, wiping out their entire civilization. three groups survived The Fall. The Craftworld Eldar, who rejected their kins hedonistic ways and fled on massive world-ships, they live for thousands of years, using special crystals to protect their souls from the chaos god they created (worn about the neck, and 'catch' their soul when they die). they follow the Eldar Path, which is a life-philosophy where they switch profession as soon as they master it, ensuring they are never bored and want for somthing to do. its all very strict and regimented. some craftworld eldar disagree with this strict lifestyle and leave (dubbed the Path of the Outcast), and assuming they arnt consumed, eventually become Pathfinders, uber sniper/rangers who do... well, whatever they want. a Eldar on a Rogue trader would almsot certainly be a Ranger(novice) or Pathfinder (master), they have cloaking tech and energy-sniper rifles. (incase you were wondering the other two groups are the Exodites, who life peacfully in forested worlds, i cant recall how they came about, maybe colonists who were stranded on the outermost worlds when the Fall happened, and the Dark Eldar, who where among the decadent eldar who caused the Fall, but had strength of will not to have their soul ripped away all at once, instead it is slowly drained, and they have to eat souls of members of other races to preserve their life (and youth) ). as a rule they are arrogant, and consider humans as a lesser race, they think nothing of manipulating events, for their own gain. and are quite willing to sacrifice whole human worlds to protect a Craftworld. prudish they are... but the tips of their ears are a very powerful feel-good spot, to which they have little resistance.
Tau are a small empire that exists on the fringe of the Imperium, the tau are a utopian society of progress and peace, split into 5 castes, these castes denote profession, and not rank. Ethereal rule as philosopher kings, humbly for the most part. Fire are warriors. Water are translators, diplomats, mediators and are powerfully empathetic. Air are drivers, pilots and crews. Earth are labourers, scientists and artists. they devote themselves utterly to a ideal called the Greater Good, which is exactly what it sounds like. anyone or anything that serves the Greater Good is welcomed with open arms, anything that isnt is crushed at the earliest opportunity, often humans that have fallen under their sway are subject to concentration camps and/or mass sterilization unless they jump at the chance to serve the Greater Good. their weapons are perhaps the most advanced of any faction save the necrons. after the last war with the imperium, a faction of Firewarriors went rogue and split off from the rest of the Tau, if you were to play a tau, it would probably be one of them. they take a much more... practical view on the greater good (namely a view that says shoot first and welcome them with open arms *arfter* they surrender, not before). Tau have no warp-presence, making them unable to interact with it, thusly they are immune to Taint and mutation, in fact, they believe Chaos to be a human myth, some form of religious belief to justify our infighting (they see Imperium vs. Chaos as a civil war). in the same vein, their ships to not enter the warp the way imperial ships do, instead they 'dive' skipping off the 'surface' of the Warp, this makes for a safe, smooth ride, but is alot slower. as a rule, a Tau would do what seems to be for the greatest good, wether that be abandoning their allies, or sacrificing themselves. they seem humans as... crude, and in need of enlightenment, but in a patronizing, and not hostile way. they are very... at peace. more monk than berserker if you get what i mean.
@ athena; yes, they are servants of the imperial preisthood (who are forbidden from having 'men at arms') and frequently for the inquisition, hunting heretics/mutants/rogue psykers. they are basically warrior Nuns, they mostly use flame and bolter weapons, and wear power armour, they are *extremely* religious, but they are neither celebate nor required to be serious all the times, there are instances of laid back Sisters who gamble and boink and such. but most are too busy being religious for such things. the whole lot of them are closet pyros >_> they are also pretty nasty in hand-to-hand, generally speaking, they are described as being 'unsexy' (in the typical sense anyway
) due to their strong preference for martal ability over feminine charms, they are often buff and heavily scarred. most of them are very military, you cant just wander off, but run aways do happen, for whatever reason.
*grins* if your interested, you coud play a runaway Sister Repetia... they are sisters who feel they have sinned, and wish to suffer in atonement, they go into battle wearing (i kid you not) a red hood and strips of paper, and carry a 8-foot long chainsaw sword called a 'Eviscerator' sometimes fitted with a built in flame thrower (see? pyros i say!) that can function quite effectively as a anti-tank weapon, to say nothing of a squishy person. perhaps the idea of dying suicidally didnt appeal and you ran off after the rest of your squad was dead
but yeh, if you like we can discuss the various options later
and for the record, in 40k, Space Marines are genetically augmented Super Soldiers who are around 8-10 feet tall, when unarmoured, can survive pretty much anything that doesnt instantly kill them, and crush a humans skull in one hand, spit acid, eat anything from rotting rats to tree bark, survive the void of space, etc.