Short answers, pulled from the story.
The Obotrites were a confederation of medieval West Slavic tribes who lived in the territory of modern Mecklenburg and Holstein in northern Germany. Their confederation included four core tribes: the Obotrites proper, the Wagrians, the Warnower, and the Polabians proper, along with several associated groups.
The name Obotrites traces to the Slavic root meaning cheerful, lively, brave, or alert. The tribal form Bodriči would have signified "the spirited ones" or "the brave ones," with a common Slavic prefix and an ethnonymic suffix.
Yes, the Obotrites were allies of Charlemagne in his wars against the Germanic Saxons and the Slavic Veleti. Prince Thrasco led them to victory at the Battle of Bornhöved in 798, and in 804 Charlemagne awarded them land north of the Elbe in Holstein as a reward for that victory.
Pribislav was the last Obotrite prince, ruling from 1160 to 1167. He accepted Saxon suzerainty in 1167 when Duke Henry the Lion restored him to power as Prince of Mecklenburg, which ended the Obotrite regnal style and founded the Germanized House of Mecklenburg.
The Polabian language survived until the beginning of the nineteenth century in Hanoverian Wendland, in eastern Lower Saxony. Most villagers in the Obotritic area were still speaking Slavic dialects into the late fifteenth century, despite the political Germanisation that began after 1170.
The ruling clan of the Obotrites continued to govern their lands as the House of Mecklenburg, founded when Pribislav accepted Saxon terms in 1167. The dynasty ruled without interruption, except for a short break during the Thirty Years' War, until the November Revolution ended German monarchies in 1918.