"I'll protect you no matter what"
Russell is the older of two sons of a famed (but estranged) alchemist named Nash Tringham. He spent his young life in hiding with the rest of his family before being left with his younger brother at the edge of a town after their mother passed away from the stress of always being on the run. The father promised the sons that he would return for them soon but he never returned, leaving Russell to care for Fletcher on his own when he was still very young.
Though Russell has had a hard life, he still admires his father and his work. Years later, Russell stole the name of Edward Elric in order to insure obtaining the funding to complete his deceased father's unfinished research: to obtain the Water of Life by means of researching the Philosopher's Stone (this is in the light novel; in the anime, they are trying to create a Philosopher's stone using a toxic alchemic substance called Red Water which amplifies alchemy but not as much as a true stone.). The Tringham brothers - now posing at the Elric brothers - must produce a Stone for their benefactor, Mugwar, the richest man in the city of Xenotime, in return for funding. Russell tries to justify the lie to his younger brother Fletcher (now posing as Alphonse Elric, the younger brother of Edward Elric) by saying that it did not hurt anyone and that no one would ever find out before they were gone. Though the Water is for the sake of bringing a sandy barren landscape to life, the process of making a Philosopher's Stone has contaminated the land and brought on a mysterious plague that affected the respiratory systems of the population not once, but twice. The second time being at the fault of the Tringham brothers.
The two do this to honor their father's memory but to do so is to live a lie. A lie that could jeopardize not only their lives but the lives of the people that were supposed to be enriched by this breakthrough. Of course, the true Elrics find out about this charade and move in to get to the bottom of it. Russell's stubbornness and skills made it a very big chaotic challenge that the younger siblings detested. In the end, the brothers all team up together to stop Mugwar's evil scheme. A side note is that both brothers are also skilled with botany, usually combining it with alchemy.
In the anime, the Tringham brothers show up again in the city of Central. Trying to obtain books that he did not have the money for, Russell tried to put the bill on Edward Elric's tab by pretending to be him. Unfortunately, Edward is a wanted man by now and Russell and Fletcher end up arrested and awaiting execution before they are saved by two soldiers who knew the true Elrics. They meet with Edward and give him a page of their father's journal that gave the location of an underground city linked with the making of a Philosopher's Stone. The Tringhams end up continuing their research of alchemy and plants in a laboratory.
Russell by nature is very charismatic and kind to those in need. He knows just what to do and to say to gain the trust of strangers who would then defend him and the image that he presents to them. His generosity is real though he uses lies to further his cause (ie: in the case of pretending to be the State Alchemist Edward Elric to gain research funds from a private investor). He does this to gain support in order to procure security for his brother and himself in a world where they are constantly on the run. He selflessly wishes to better the lives of people through his research but he can be quite arrogant and cocky, especially with those that he dislikes at the same time. He is not hesitant to openly mock someone that he looks down upon, calmly jabbing at any insecurities with an almost too-easy air. However, he will take risky actions to bring down his opponent once his own buttons have been pushed.
Though he works hard and gains tremendous amounts of knowledge at a young age, he does not have his own goals but seeks to complete those of his father. He is stubborn and is very difficult to reason with even when what he is doing is completely wrong, chained by responsibility to family honor and expectations. He does not seem to realize that this mindset hinders him and he often wears a mask of indifference when it is pointed out. It is clear from other parts of his personality that it is not a true indifference but it is unclear just what moral dilemma he would face especially if all of it is eclipsed by the very pressing desire to keep Fletcher and himself safe. He is confident that his plans will work and that the results would justify the means. He is so wrapped up in his own head when it comes to certain ideals that there is no way to convince him to let go of them.
He is highly protective of his younger brother Fletcher and will do anything and everything to make sure that he is safe. He puts his brother above everything and everyone else though he also does his best to treat him as a capable person who carries equal weight in helping with the research that they do. He tells Fletcher that he should run away if anything should go wrong and that he (Russell) would protect him no matter what. However, perhaps it is Russell who is the one who needs protecting as the chains of responsibility and obligation continue to weigh him down, suffocating him unaware of his precarious position.
Russell is an alchemist. In Fullmetal Alchemist, this means he can preform transmutation, the ancient metaphysical science/mystical art of manipulating and altering matter by using natural energy focused with an array (unless you're special and have seen The Truth like Edward Elric, etc). Transmutation consists of three steps:
1) Understanding the inherent structure and properties of a material to be transmuted.
2) Deconstructing the material using natural energy to reform it.
3) Reconstructing the material into a new shape/form with the energy used to deconstruct it.
Alchemy is governed by the law of equivalent exchange: what you put in is what you put out. You can't make an entire table out of a sheet of paper, you can't bring dead things back to life, but you can probably make a stone chair out of a boulder or something like that. Of course Bending doesn't follow equivalent exchange and that hurts his brain somewhat and he prefers to use Bending as he would alchemy.
Oh, and Russell is also a botanist so he studies plants. He has successfully combined his two areas of studies into one and can manipulate how plants grow using alchemy (ie: catching bullets with vines as seen in the light novel, making trees grow to enormous sizes to suck up toxic water in the anime)