It wasn't until he told Vishtaspa that he could heal his ailing horse that Vishtaspa gave him a chance. After curing the horse, Zoroaster had his first convert. Vishtaspa then changed the religion of his "kingdom- to the teachings of Zoroaster.
After Zoroaster's death, many changes occurred. It got to the point that some followers of Zoroasterianism began to worship Zoroaster himself. Over time, the stories of Zoroaster's life were exaggerated until things like his birth and the curing of Vishtaspa's horse became legends in themselves. Another glaring change that occurred was that Zoroastrianism became less monotheistic. One example is that of the spirit Mithra. Zoroaster more or less didn't concern himself with Mithra, but after his death, Zoroaster's followers "reinstated- Mithra into their religion. Another change, and one that would have angered Zoroaster was the fact that people once again began using haoma and making animal sacrifices to Zoroaster.
Jesus' intentions were different from those of Zoroaster in that Jesus made a concentrated effort to show people that his way was the only way to eternal happiness in heaven. Zoroaster didn't seem concerned with making everyone believe that his way was the only way to eternal happiness. Instead, Zoroaster just changed around many of the common beliefs of the time. Jesus' intentions were to spread his word and convert people to Christianity and (Judaism) and show them that repenting their sins was the only way to eternal happiness. Jesus used parables to illustrate his points to the people. This way he made it easier for his listeners to relate to the lessons he was trying to teach.
Jesus' success is obviously still very much evident today. Although he was ultimately crucified for being the king of Jews, the message he spread can only be looked at as an extreme success. At the time of his crucifixion he had converted many people, but it wasn't until after his death and resurection that more and more people began to believe in his message.