Many mythologies have deities whom either personify the earth or sky (e.g. Gaia and Uranus). However, are there any deities that represent other realms, like how Tartarus is the personification of Tartarus? Also, please take note that by "realms", I mean places that are inhabited (e.g. Asgard of Norse mythology, Aaru of Egyptian mythology) and not places such as the sun or moon.
Hel personified and rules the "bad" afterlife in norse mythology. In fact, she took her name from it. There has been speculation that she as a mythological figure was an invention by Snorri, however, as other sources always talk about figures being "in Hel".
Margaret Clunies Ross says that most poetic contexts are not sufficiently clear for us to distinguish between Hel as a place and Hel as "the personified guardian of that place", and that she and her attributes are "tangliable" personifications. (I'm translating back from a translation of Prolonged Echoes, so the quotes are likely not exact).
Tutelary deities that personify or protect places are very common around the world. The Romans had major tutelary deities or their cities, the well-known Capitoline Triad for instance, but also on smaller scale with Lares Compitales, guardian deities of neighborhoods, and Genius Loci.
Chinese folk religion is rife with place-bound tutelary deities. Notably, the Dragon kings of the four seas, and the Chenghuangshen (city gods), along with gods or river, mountains, towns, etc. Similarly, the Hindu Gramadevata, as well as numerous others, especially shamanistic and folk religions.
The underworld is envisioned in many different ways, but there is usually some deity that serves as it's representative. Examples include: Ereshkigal, Hades, Yama, Satan, Hel, Mictlantecuhtli, Izanami, Osiris, Xibalba, Hine-nui-te-pō, etc.