Rav Naftali Zvi Yehuda Berlin (1816 - August 10, 1893), known as the Netziv, was the Rosh Yeshiva of the famed Volozhin Yeshiva for almost 40 years, until it was closed by the Russian government in 1892.
His hasmada was legendary. Once asked if it was true that he learned twenty hours a day, he said he only learned sixteen hours a day. However he added that he did this every day including Friday, Shabbos, and Yom Tov for 25 years straight. On his wedding day he was no where to be found. They finally found him in the local Beis Medrash as if it were an ordinary day. He quickly washed up and changed and was taken to the Chupah.
The Netziv was the quintessential success story. Not very gifted as young child, his parents decided to take him out of cheder and teach him a profession. Upon hearing this plan the Netziv burst out in tears and begged for one more year to prove himself. And prove himself he did. He later said that had he not shed those tears, in Shamayim they would have brought him a copy of the his sefer with his name in it as the author, and explained to him that this was his destiny that he lost out on for not applying himself to his fullest.
You may be interested in this picture of the Netziv:
The Netziv's biography is available from Artscroll.