So I´ve gotten most of the mechanics down, and are working on the fluff. Here is the basic outline of what I had in mind for the character, feel free to comment and offer suggestions, I´m not all that well-versed in the deeper parts of the lore.
He was raised on a remote research station as the son of a guardsman and a scientist and showed a sharp intellect pretty early in life, and it was planned that he would follow in his mothers footsteps as a biologist. His youth was cut short though, as the station came under attack by a host of indigenous aliens. The station managed to hold them off long enough for a nearby strike force of Dark Angels to arrive, but most of its inhabitants were slain, including both Elyas parents. With nowhere else to go, and having shown great courage in the defense of the station despite his age, he was offered to join the legion. He would pass through his trials until he was sent back to his home to search for and eradicate any traces of the aliens, which he did, and as such became a neophyte of the Dark Angels. He continued to serve faithfully until he was accepted as being worthy of becoming a true marine. He would serve his legion well, often in roles outside of the traditional infantry line like a scout or saboteur. With an aptitude for military intelligence, he would eventually come to serve in the Firewing, the most hidden of the Dark Angel orders.
While many skills that I want is unavailable at Rank 1, I imagine Elyas as serving a versatile tactical role. With bolter specialization and specialized ammo, he can operate well against many different foes, serving as long-range marksman or short-range devastator. I didn´t take it from start, since I wanted to add some skills for more diversity to him, but I plan to take the Astartes Weapon Specialization talent asap. Also, and hopefully there can be some way to incorporate a good reason for this, I would want to take the Guerrilla Training talent as an Elite Advance. I´m not looking to become a stealth master or anything, but the innate penalties of power armor makes any kind of stealth hard. I might also want to look at getting the Infused Knowledge talent to capitalize on having a pretty good Intelligence, but that is not exactly top priority.
Edit: Oops, realized if I wanted you to take a look at this, I should probablt include an @Trish_the_Nugg_Queen