A helicopter comprising: - a fuselage with a nose; - a main rotor fitted to the top of said fuselage; and - an anti-torque rotor fitted to said fuselage on the opposite side of said nose; said anti-torque rotor comprising: - a supporting body; - a drive shaft which rotates about a first axis with respect to said supporting body; - a hub connected operatively to said drive shaft and angularly rotatable together with said drive shaft about said first axis; - at least one pair of blades which are connected operatively to said hub, are angularly rotatable together with said hub about said first axis, and are angularly rotatable about respective second axes and with respect to said hub to adjust the pitch angles of said blades; and - an actuator which can be operated to rotate said blades about said respective second axes to adjust the pitch angle of said blades; said actuator in turn comprising: - an electric motor which generates torque along said first axis; and - a mechanical stage designed to convert said torque into rotation of said blades about the respective second axes; a single said mechanical stage being interposed between said electric motor and said at least two blades; said single mechanical stage comprising: - a rotary member which rotates about said first axis, and is rotated about said first axis by said electric motor; and - a sliding member which translates along said first axis, is fitted to said rotary member, and to which said at least two blades are hinged; said electric motor being fixed to said supporting body; said rotary member defining a first threaded surface, and said sliding member defining a second threaded surface which meshes with said first threaded surface; said actuator further comprising a linkage interposed between said sliding member and said blades to convert translation of said sliding member along said first axis to rotation of said blades by the same angles about said respective second axes; characterized in that said electric motor comprises: - a stator which is annular with respect to said first axis; - a rotor connected electrically to said stator and rotatable about said first axis by an electric torque generated by stator; and - a housing fixed to and projecting from said supporting body and housing said stator and rotor; said electric motor being arranged outside said fuselage and external to said drive shaft, said blades and to said hub; said linkage further comprising: - a body fitted to said sliding member and which rotates with respect to said sliding member about said first axis; and - two levers which are hinged to said body about respective third axes, and are hinged to roots of respective said blades about respective fourth axes; said body being movable integrally with said sliding member in a direction parallel to said first axis, and being located radially outwards of said sliding member with respect to said first axis. - a fuselage with a nose; - a main rotor fitted to the top of said fuselage; and - an anti-torque rotor fitted to said fuselage on the opposite side of said nose; - a supporting body; - a drive shaft which rotates about a first axis with respect to said supporting body; - a hub connected operatively to said drive shaft and angularly rotatable together with said drive shaft about said first axis; - at least one pair of blades which are connected operatively to said hub, are angularly rotatable together with said hub about said first axis, and are angularly rotatable about respective second axes and with respect to said hub to adjust the pitch angles of said blades; and - an actuator which can be operated to rotate said blades about said respective second axes to adjust the pitch angle of said blades; - an electric motor which generates torque along said first axis; and - a mechanical stage designed to convert said torque into rotation of said blades about the respective second axes; - a rotary member which rotates about said first axis, and is rotated about said first axis by said electric motor; and - a sliding member which translates along said first axis, is fitted to said rotary member, and to which said at least two blades are hinged; - a stator which is annular with respect to said first axis; - a rotor connected electrically to said stator and rotatable about said first axis by an electric torque generated by stator; and - a housing fixed to and projecting from said supporting body and housing said stator and rotor; - a body fitted to said sliding member and which rotates with respect to said sliding member about said first axis; and - two levers which are hinged to said body about respective third axes, and are hinged to roots of respective said blades about respective fourth axes;