Transcriptional repressor involved in multiple aspects of cortical development, including neuronal migration, laminar and areal identity, and axonal projection (PubMed:25232744, PubMed:30250039). As transcriptional repressor of FEZF2, it blocks the formation of the corticospinal (CS) tract from layer 6 projection neurons, thereby restricting the origin of CS axons specifically to layer 5 neurons (By similarity). {ECO:0000250|UniProtKB:Q64336, ECO:0000269|PubMed:25232744, ECO:0000269|PubMed:30250039}. This is the function of Ensembl gene identifier ENSG00000136535 (TBR1, T-box brain transcription factor 1).