Chimeras

[The Truth]

A Chimera, as understood in the Fullmetal Alchemist series, is a creature synthesized by alchemically "marrying" two or more dissimilar living beings into a new, complete form displaying attributes of its "components". Though a legitimate branch of bio-alchemy, chimeric research has seen very few significant strives in Amestrian history - or at least in recorded history - and has been described as a science built upon countless dead ends and false starts. Still, the production of such fantastical beings is possible with the proper alchemical expertise and skill (as displayed by both Shou Tucker, who had made chimeric alchemy his focus as a State Alchemist, and Cornello, who was able to perform chimeric alchemy with the aid of an incomplete Philosopher's Stone).
As mutant beasts granted the traits of multiple species, standard chimeras appear best suited for guard duty and are frequently positioned as such.


Human Chimera
While the synthesis of chimeras is an accepted, albeit rare and elusive branch of alchemy, the concept of extending its mutative hand to the realm of human characteristics and abilities falls under Human Transmutation and is therefore strictly banned as a practice under the authority of the military. On the other hand, though there are alchemists who flout this decree and step across the threshold into monstrous experimentation, it has been publicly stated that all illicit attempts to create a human-animal hybrid have failed. This is an untruth.
State Alchemist Shou Tucker has been accredited with the creation of the first chimera capable of human speech, but the truth of the matter is that his creation was actually a crude Human Chimera created in secrecy and passed off as an advanced standard chimera to achieve his state certification. It was only during his second attempt at this that brought his transgressions to the government's attention. However, the State Military itself has been experimenting with synthesizing Human Chimeras in secret laboratories for some time, with limited success.

Human Chimeras similar to those created by Shou Tucker are marked as failures by the military, having very little social ability and significantly warped forms while experiencing high levels of physical pain due to having internal systems that are incomplete or otherwise insufficient for maintaining their new hybridized bodies; still, having been human at one point, their souls and memories remain largely intact, despite a limited ability to convey their feelings and thoughts to other humans. A step above these complete failures are chimeras that maintain much of their original human forms but with added physical traits that enhance their physical abilities while making them incapable of blending in with society as normal human beings.
Human Chimeras that are deemed "successes" by the State Military belong to two categories as well. There are those with entirely human outward forms whose internal makeups have incorporated increased senses, versatile physical structures and abilities identical to the animals with which they have been alchemically spliced, granting them superhuman traits while maintaining an inconspicuous shape. However, the form which the military seems to have accepted as their ultimate success in regards to the creation of Human Chimeras are those capable of transforming from full human form to that of a man-beast hybrid and back at will.