It is an NPN transistor ( the control device). A diode is a diode and only a diode it is a pn junction ( in its native form).
The diode is used to divert high pulses that could cause a breakdown of the transistor junctions , often a diode is also placed acros the motor conduting spikes away from the collector to the supply rail.
The shown diode circuit seems meaningless, apart from the special case, that the motor is externally driven with no supply, respectively the motor keeps rotating due to inertia and the supply is shut down. In this case it would protect the transistor.
It's not what wikipedia calls a diode snubber, usually known as freewheeling diode.