Yissachar יששכר

Leah's fifth son; she gave the name: "God has given me my reward." Jacob said of him something odd at first hearing: "Issachar is a large-boned donkey, couching down between the sheepfolds… and he bowed his shoulder to bear." Rashi reads it as praise: the yoke he took on his shoulder is the yoke of Torah.

Chronicles bears it out: among those who came to David at Hebron were "of the sons of Issachar, men who had understanding of the times, to know what Israel ought to do; their heads were two hundred, and all their brethren were at their commandment." The sages understand "understanding of the times" as mastery of the calendar: the reckoning of months and years on which every festival depends.

With this goes the famous pairing of Issachar and Zebulun: Zebulun goes out to trade and provides, Issachar sits in the tents and learns, and the reward is divided equally between them. The arrangement still bears their names.