Destiny always appears as a bald and meek little old man in a hooded cloak, leaning on a warped cudgel. His eyes change color often and he always appears friendly unless his purpose is confrontation. The only being he has ever shown aggression towards is Chaos. In battle he can appear at any size.
Destiny governs all paths of fate in the universe and has heralds that go on missions for the balance of good and evil.
As Destiny explains, he does not control fate or the choices of others, rather he is fate itself. He is the outcome of peoples actions even though that may change. Destiny is the existance of every fate in the universe.
Destiny's powers are vast and cosmic and include event control. With event control, he can control the outcome or even the target of any localized event. The occassional brute will misjudge the meek appearance of Destiny and attack, much to their own distress. You can learn more about lord entities under True Gods.