Born in 1905 in Zawalow, Austria, (now part of Ukraine), Nachman Avigad made aliyah in 1925 and received his master’s and Ph.D. in archaeology from Hebrew University. He participated in digs at the Beit Alpha and Hamat Gader synagogues, then directed the excavations at Beit Shearim, where he personally identified the family tomb of Rabbi Yehuda HaNasi, the redactor of the Mishnah. Nachman Avigad also published the last of the Dead Sea Scrolls, excavated the mountain fortress at Masada, authored numerous articles – especially on Hebrew seals – and identified a seal belonging to the Israelite queen Jezebel (the identification has been contested, but I’m placing my bet with Nachman Avigad).Avigad was one of the premier Northwest Semitic epigraphers of his generation. He published one of the Dead Sea Scrolls (the Aramaic Genesis Apocryphon) but this was not the "last" of the Scrolls, whatever that means. It was found in Qumran Cave I. Also, it may be that he did some work at Masada, but Yigal Yadin was the chief excavator and Avigad is not on Yadin's list of staff members of the expedition. Perhaps a reader knows the details and can fill us in. Many of the Hebrew seals Avigad published were unprovenanced and some of these are probably forgeries. I have no particular view one way or another about the YZBL seal.
UPDATE (25 October): Reader David Stacey e-mails: "Jim - see IEJ 7 (1957) pp 1-60. - The Survey and Excavation of Masada 1955-56 - Avi-Yonah, Avigad, Aharoni, Dunayevsky, and Gutman." Also, I see I commented on the YZBL seal in a post back in 2007.