Doctor Moira Vahlen:

The scientist in charge of XCOM's research division. She expresses an unusual enthusiasm towards adapting alien technology to forward human scientific advancements. All aliens captured alien are to be delivered to her lab per the doctor's request. Dr. Vahlen is also a member of the commander's advisors.

Doctor Raymond Shen:

Dr. Shen is the head engineer of XCOM's development team and the creator of the A.I. matrix in each base. He is one of the more senior members of XCOM with decades of experiences and is world renowned. His views on the extent in which XCOM should utilize alien technology often conflicts with Dr. Vahlen. Dr. Shen also advises the commander on alien materials and components.

Central Officer Bradford:

Bradford is the second-in-command in the XCOM project and is in charge of the organization's communications across the several bases and organization on the more specific level. All Base Commanders report to Bradford. He is dedicated to ending the alien menace and helps the commander with battle strategy.

Spokeman:

A mysterious figure that represents the council of nations responsible for funding the XCOM Project. All council concerns and request will be voiced through him as well as a monthly report on the organization's effectiveness as a whole.

XCOM Commander Martin Anderson:

The commander is the head of the XCOM project and responsible for all major decisions including research and strategy. A veteran of conflict in the middle-east, Commander Anderson was selected for his flawless record and comparatively young age. He often keeps to himself when not over-seeing missions but is incredibly charismatic and intelligent.

Skyranger:

The Skyranger is XCOM's primary method of troop transport. A vertical take-off jet, it can hold up to eighteen soliders and land in urban areas for fast response times.

Raven:

The most advanced fighter jet developed by XCOM, it is capable of operation in the upper atmosphere. Its speed and maneuverability are the main strengths of the Raven coupled with the avalanche missile system.

A latent mental power existing within certain individuals. As demonstrated by the Aliens, it has the power to be used as an devastating weapon in combat. As of present, XCOM has very little understanding of this power and even less on it's implication.

A nano-material that can be used to augment human abilities or change them to interface with a heavy much suit. Efforts to replicate it has so far proved futile and thus it is incredibly rare. That is why the augmentation are reserved for the top performing operatives. Those selected for augmentation will be alerted when the lab is ready for them. On the other hand, only volunteers are taken for the implementation of the cybernetics need to operate a much suit.

Infantry:

The core of XCOM's miliary personnel, those with this specialization are focused on medium range engagements. Their primary weapons are usually carbines, assault rifles, and battle rifles. They perform multiple roles on the battlefield and as such are good overall.
Assault:

Close-quarters specialists who primary role is to breach structures and break-through enemy lines. Their primary weapons are usually assault rifles, sub-machine guns, and shotguns. They also come outfitted with a sword for engagements with aggressive aliens or silent take-downs.
Demolitions:

Operator who handles high-explosives such as C4 and rockets. They specialize in taking down hard targets or clearing out large structures. Their primary weapons are assualt rifles, smgs, or carbines. The payload of their explosives varies per mission but C4 and a rocket launcher are always part of their equipment.
Gunner:

The soldier with the biggest gun on the battlefield, they are tasked with holding key positions and suppressing enemy fire. Their primary weapons is the heavy machine gun and a smg. They are also given thicker armor since the classes requires much strength.
Scout:

Specialists in remaining undetected by enemy forces, their role is to spot targets and report intel back to the squad. Their primary arms are battle rifles, assault rifles, carbines, and smgs. A scout is required on every mission.
Medic:

Field-doctors trained in fast, effective treatment and ensuring the safety of the squad. Their training is similar to infantry. Primary arms include assault rifles and smgs. A medic's main tool is the special med-kit developed by XCOM, able to stop bleeding immediately and numb pain.
Sniper:

The best marksmen in XCOM, snipers give covering fire to the squad and work with the scout to mark targets. Their primary weapon is a sniper rifle and a smg.

Specialist:
These operatives have a direct link to the base's A.I. matrix and are able to quickly scan and hack into enemy systems. Their primary weapons are smgs, shotguns, and assault rifles.

Engineer:
Engineers carry portable emplacements such as small auto-turrets and mobile cover. Their primary weapons include assualt rifles, carbines, smgs, and shotguns. They are also responsible for retrieving alien devices and tech.

Ranger:
Experts in melee combat and sneaking behind enemy lines, these soldiers are not afraid to get up close and personal. Primary weapons are smgs and shotguns. Additional equipment includes a full-length sword and an expanding small shield on either arm, however they generally have lighter armor.

Every class comes equipped with a combat knife and a side-arm, which you can choose. I might allow a couple people to be interceptor pilots if they are really interested.
(More classes will come as the RP progresses and changes will be available)