And I looked, and behold, a white horse! And its rider had a bow, and a crown was given to him, and he came out conquering, and to conquer. (Rev 6:2)
The four horses in Revelation 6 represent four threats: conquest, bloodshed, famine and death. The riders do not seem to represent any specific people. Rather the rider and horse together represent these four threats. The imagery of the four horsemen comes from Zechariah 1:8-17; 6:1-8.
There is another white horse in Revelation 19:11 whose rider is clearly Jesus (see Rev 19:11-16). However, there appears to be no direct connection between the two passages apart from the fact that they both describe white horses.