He told a lot of lies but they are eventually come true.He said pirates were attacking the village and when he was introduced pirates attacked the village,He said he knew giants and he met giants.He said he found an island but discovered it was actually poo from a giant gold fish I can’t remember if the island part was true but we did eventually see a giant goldfish.He said he had an army of a thousand pirates under his command and in one episode a lot of pirates started worshiping him as a god, he also said he went to an island full of dwarfs.Now he did actually come across a ship commanded by a thousand or so people who were very small.Now a recent lie is that he is a descendant of noland the liar.This is kind of another theory as well.Noland and ussop have a lot in common they are both considered liars, they both have the same eyes and an important thing is ussop is always seen wearing an armband that is blue and white stripped the only other time this is seen is by noland when he wore pants of the same design.Now none of this is really hard proof but oda is known for his foreshadowing.When noland was introduced they focused a lot on ussop in that scene especially whenLuffy became convinced that noland and ussop were the same person to which ussop replied that they are not and that they don’t even have the same name.We also learned that most of noland descendants have disregarded the name and most don’t even know they are related.As of now we have never learned of ussop name, the only people who names we don’t know is ussop formerly sanji and nami. Nami lost her family in a war and was adopted as a baby, sanji turns out to be a vinsmoke so that just leaves ussop.Finally the last piece of evidence is the family trait. It was said every descendent of noland has a calling to the sea. Yassop said he always wanted to travel the world and be a pirate and told luffy that leaving his family was the hardest thing he ever did but he just could not resist the call of the sea anymore.
Ussop also went on to say he felt a calling as well and he needed to be a pirate.
All this points down that ussop will turn out to be a descendent from noland