Rav Avraham Mordechai Alter (December 25, 1866 - June 3, 1948), better known as the Imrei Emes, was the third Rebbe of Ger Chasidus, a position he heled from 1905 until his passing 43 years later. Before the war, the Imrei Emes had an estimated 200,000 followers.
After his father's passing, when asked to be the next Rebbe, the Imrei Emes responded, "I am unworthy of being the representative to the king. And so now you will all have to fend for yourselves." The chasidim were so taken by his humility that they urged him even more, and after much cajoling, he finally agree to be their Rebbe.
You may be interested in this picture of the Imrei Emes:
The Imrei Emes's biography is available from Artscroll.