Transcriptional repressor that plays a central role for embryogenesis and the pluripotency of embryonic stem (ES) cells. Sequence-specific DNA-binding factor that represses gene expression in pluripotent ES cells by directly binding to key genetic loci and recruiting epigenetic modifiers. Interacts (via coiled coil domain) with HCFC1. May be regulated by shuttling of the protein between the cytoplasm and nucleus. Mainly restricted to pluripotent cells of the developing embryo, to oocytes, and to certain regions of the adult brain. First appears at the 2-cell stage, intensifies during the 8-cell and compact morula stages, but subsides in the blastocyst. Mice show periimplantational lethality and have defects in the inner cell mass. Conditional knockout prevents the growth of ES cells while forced expression allows ES cells to proliferate without differentiation under conditions that normally do not promote self-renewal. Was named 'Ronin' (a masterless Japanese samurai) by PubMed:18585351 because of its lack of apparent relationship to known 'master' regulator of pluripotency. Belongs to the THAP11 family.