U.M.B.R.A.'s leader is a man called Van Buren. The bio I wrote awhile back goes like this: "Van Buren used to be a colleague and a close friend of the Chancerys. (Faith's parents if you're paying attention). Eventually, his greed caused him to turn on them, intent on obtaining the powerful weapons components they recently unearthed on for himself, to sell to the highest bidder. He has used the wealth he stole from his former allies while working with them to establish a vast network or spies, as well as a cadre of formidable warriors who will stop at nothing to stop Faith and attain the weapon components for their master." Thus far, we've only seen a couple members of this cadre, but there are many more to come, as Van Buren is more of an office CEO-type. But, like any terrorist organization, UMBRA has its share of grunts.
A quick note on the origin of UMBRA (in case you're wondering where the Hell we come up with stuff); UMBRA was a name John came up with in our Secret Monkey days as an evil organization that was the nemesis to SQUAD, which was our send-off of Marvel's SHIELD, well before Samuel L. Jackson became the leader of those guys. UMBRA just sounds kind of bad, but it was intended to be kind of jokey, at first. Ah, well, you can't always be funny.