If other people can put forth stupid suggestions like Riou or Jowy as the father then i bet it's Lazlo!! Or not!
Seriously, I was playing suikoden III and ch 2 of Hugo when Lucia mentions his father and was thinking. When he gives Hugo his black hair tips and that he was someone we met in suikoden 2 and according to Lucia he was "fine man". My main bet would have to General Hauser. He's got black hair, same race Lucia if that mattered to her, he's a great man and real solider and warrior probably her type. He was down in Tinto for awhile during the war, which isnt far from the Grasslands at all... guess it as good as anyone else speculation...my second guess i'd probably put my money on Han Cunningham...those choices are aleast semi-logically compared to some of the answers i read in this thread...lol
I will establish one mighty nation in this land... a single, powerful nation, born of force and wielding force... that's the one and only way of freeing this land from war.
Unleashing True Runes https://youtu.be/Q7Ry1WmNMNg