Voltage Controlled Variable Resistor

Does anyone know of an IC chip or discrete component intended to be used as a variable resistor whose resistance value may be controlled by either varying its voltage input/signal or changing a pulse width modulated signal to change its resistance.

I wanted to control a bi-directional motor (can rotate CW or CCW direction with variable speed) remotely using radio control used on RC Planes/cars whose pulse width modulation varies from 1.0 to 2.0 milliseconds, 1.5 being the neutral - or resting mode. The motor should be able to turn from very small increments to really fast speed depending on the amount of control signal being applied. It also should operate exponentially NOT LINEARLY (with ease-in and ease-out) meaning it should start slow, then gradually move very fast but then deccelerate slowly to a smooth stop not abruptly.

Instead of redesigning a motor controller, I was thinking of using an RC servo motor, taking apart the gear asm and instead of controlling the servo motor movement using pulse width to turn it CW and CCW (which limits its rotational movement to only 90 degrees as most servo motors do using its built-in gear asm, I instead would remove the gear asm, fixed the pulsewidth signal to 1.5ms, and control the motor movement direction and speed by changing the variable feedback potentiometer's position.

This is where the voltage controlled variable resistor will come into play. Instead of moving the pot mechanically, I want to control it electronically. Hope you can help. Thanks in advance for any ideas.