Joseph Smith was killed by a mob while awaiting trial on spurious charges at Carthage Jail in Illinois. The armed mob of men with painted faces stormed the jail and shot him and his brother Hyrum to death.. The Wikipedia article on the subject provides a lot of detail about the subject, a link is provided.
Brigham Young! He had way more children than Joseph Smith. Thus, Young had more Mormon descendants to further the Mormon movement . Brigham also didn't die as early as Joseph Smith, giving him more time to reign over "Zion"ANOTHER ANSWER:As there wouldn't be a Mormon movement without Joseph Smith, I'm going to say that he contributed more... he started the whole thing!
Elias Smith - Mormon - died in 1888.
Ronald Joseph Smith died in 1995.
Joseph B. Smith died in 1861.
Joseph Smith - bobsleigh - died in 1983.
Joseph Smith - preacher - died in 1792.
Joseph Lindon Smith died in 1950.
John Smith - uncle of Joseph Smith - died on 1854-05-23.
Joseph Smith III died on 1914-12-10.
Joseph Smith Harris died on 1910-06-01.
Joseph Smith Jessop died on 1953-09-01.
Joseph Showalter Smith died on 1884-09-28.