Rav Meir Katzenellenbogen the Maharam Padvi was the first of the name, having been born in Katzenellenbogen in the late 15th century CE, studied in Prague, and lived in Padua where he married the daughter of Rav Avrohom Mintz. He was a cousin of the Ramo, and a great Torah scholar in his own right. He has many descendants today, among a number of families of rabbinic ancestry, including my own.
The family is descended as well from Rashi, and thus from Dovid Hamelech, which might answer the first question, and put the name among other families such as Shapira, Treivish, Loew, Landau, Frankel, Wahl, and many others who share the ancestry.