NGC 6166 is a supermassive, type cD galaxy, with several smaller galaxies within its envelope.
Suspected to have formed through a number of galaxy collisions, NGC 6166 has a large number of globular clusters (estimated as between 6,200 and 22,000 in 1996) orbiting the galaxy. A 2016 study, however, gave an even higher number (around 39,000) suggesting also that the halo of this galaxy blends smoothly with the intra-cluster medium. Because of that, the galaxy has the richest globular cluster system known. The galaxy harbors a supermassive black hole at its center with a mass of nearly 30 billion M☉ based on dynamical modeling.
NGC 6166 is known to host an active nucleus, classified as an FR I source, which powers two symmetric parsec-scale radio jets and radio lobes and it is caused by the infall of gas into its center caused by a cooling flow that deposits 200 solar masses of gas every year there.
It has been proposed that a number of O-type stars may be present in the center of NGC 6166.