Histone demethylase that specifically demethylates both mono- and dimethylated 'Lys-9' of histone H3. May act as a transcription regulator controlling hair biology (via targeting of collagens), neural activity, and cell cycle. 2 2-oxoglutarate + N(6),N(6)-dimethyl-L-lysyl(9)-[histone H3] + 2 O2 = 2 CO2 + 2 formaldehyde + L-lysyl(9)-[histone H3] + 2 succinate Binds 1 Fe(2+) ion per subunit. Contains two Leu-Xaa-Xaa-Leu-Leu (LXXLL) motifs. The LXXLL motifs are essential for the association with nuclear receptors (PubMed:14570920). The JmjC domain and the C6-type zinc-finger are required for the demethylation activity.