Gamaliel is the ninth Qlipha, the shadow of Yesod, the sphere of the Foundation. Read as "the obscene ones" or "the polluted of God", it is the corruption of the foundation and of the astral and generative life.
In the scheme followed here it is ruled by Lilith, who is also the name given to the tenth and lowest shell in this same list; the doubling is not an error in the source material but reflects Lilith's standing, across the older Jewish sources, as the qliphothic tradition's most fully developed figure, first named as a night demon in Isaiah 34:14, elaborated in the Babylonian Talmud (Niddah 24b, Eruvin 100b, Shabbat 151b) as a winged, long-haired demoness, and given her fullest early narrative in the medieval Alphabet of Ben Sira as Adam's first, rebellious wife. Her presence ruling both Yesod's shadow and Malkuth's own suits a figure whose Jewish literary history already spans sexuality, the night and the generative and material world well before any ten-fold qliphothic scheme existed. Spellings and rulers of the shells vary by source; the material is presented academically.
Yesod is attributed to the Moon, and Gamaliel's corruption of the foundation is read as the Moon's own governance of the astral, reflective and generative life turned obscene, image and instinct detached from the higher sephiroth they are meant to transmit.
Sources Encyclopaedia Judaica, 2nd editionMichael Berenbaum and Fred Skolnik (eds.) with The Golden Dawn: The Original Account of the Teachings, Rites, and Ceremonies of the Hermetic Order of the Golden Dawn, 6th editionIsrael Regardie