Martin Chemnitz (Kemnitz) is often referred to as "the second Martin." After Martin Luther's death, he was instrumental in unifying Lutherans in Germany, who had become divided over theological issues. One of Chemnitz's publications well known to Lutherans is the Book of Concord.
Portraits of Chemnitz, such as the one here, show him holding a set of beads, thought to be a type of prayer beads. Replicas of these beads are known as the Chemnitz prayer beads. You may download here a copy of the associated practice, which appears on the Chemnitz Fraternity web site.