Rav Elchonon Wasserman (1874 - July 6, 1941), a close disciple of the Chofetz Chaim, was probably the only Rosh Yeshivah who would teach Gemara by concentrating on the simple pshat - explanation of the written word. In his younger days, he had been known as a genius in pilpul. However, a leading Rosh Yeshivah advised him, "This is not the way. One must concentrate on pshat!" It was no easy task for Rav Wasserman to tame down his racing mind. But once he had accepted the advice, he disciplined himself until he eventually became recognized as a "Gaon in pshat."
We knew that he practiced Shivisi HaShem L’Negdi Tamid (”I always envisioned G-d before me”). For that reason, he absolutely never laughed or smiled. The only exceptions were when a mitzvah called for rejoicing, such as at a wedding; also, when he would quote the Chofetz Chaim, his face would relax into a slight smile. As part of this severe self-discipline, he would never slip a hand into his pockets. During the most biting cold of winter, his hands - red and frozen - would be gripping his coat buttons.
Rav Elchonon Wasserman's biography is available from Artscroll.