Oxygenase that can act as both a histone lysine demethylase and a ribosomal histidine hydroxylase (PubMed:23103944). Specifically demethylates 'Lys-4' (H3K4me) and 'Lys-36' (H3K36me) of histone H3, thereby playing a central role in histone code (By similarity). Preferentially demethylates trimethylated H3 'Lys-4' (H3K4me3) and monomethylated H3 'Lys-4' (H3K4me1) residues, while it has weaker activity for dimethylated H3 'Lys-36' (H3K36me2) (By similarity). Acts as a regulator of osteoblast differentiation via its interaction with SP7/OSX by demethylating H3K4me and H3K36me, thereby inhibiting SP7/OSX-mediated promoter activation (By similarity). Also catalyzes demethylation of non-histone proteins, such as CGAS: demethylation of monomethylated CGAS promotes interaction between CGAS and PARP1, followed by PARP1 inactivation (By similarity). Also catalyzes the hydroxylation of 60S ribosomal protein L8 on 'His-216', thereby playing a role in ribosome biogenesis (PubMed:23103944). Participates in MYC- induced transcriptional activation (PubMed:17308053). {ECO:0000250|UniProtKB:Q9JJF3, ECO:0000269|PubMed:17308053, ECO:0000269|PubMed:23103944}. This is the function of ENSG00000170468 (RIOX1, ribosomal oxygenase 1).