Raiden is likely one of the most important old men in the MK11 story. He has been a central figure for a long time in the Mortal Kombat series. His wisdom and power are crucial in the fight against the antagonists.
Well, without more specific details about which 'old man' is meant in the MK11 story, it's a bit difficult to be precise. There are some old - looking or aged characters like Shang Tsung who has been around for a long time. He has his own motives and schemes that are intertwined with the overall plot of the game. He might be the one you're referring to if the 'old man' is a devious character.
Since we don't have much information about this specific 'blackkklansman old man story', it's difficult to say who the old man is. He could be a fictional character created to represent the older generation's experience with the KKK - related events in a story based on 'BlacKkKlansman'.
In 'the old man at the bridge story', the old man is an ordinary person whose life has been upended by war. He seems to be a bit forlorn and lost. He has his own little world back home with his animals, but now that world has been destroyed by the war. He is at the bridge, a sort of liminal space between the past and an uncertain future. He represents the countless individuals who are displaced and left in a state of confusion and despair during times of war.
There's not enough detail to know for sure who the old man is. He could be a variety of things. He might be a war veteran who has some skills or knowledge that comes into play in the story. Or perhaps he's an old family friend of one of the characters, and his presence in the story is to provide a different perspective or a connection to a past event that is related to the events in 'Equalizer 2'.