It was also known under several names. In roman times the bar was called Dies Irae (latin, means Day of Wrath), while in Merlin times it was called Avalon.
It was probably founded and owned by Lilith herself. For some time man and his wife, operated it for her. They would later become (with hellp of Hern the Hunter and John Taylor´s minor one) being known as the Lamentation.
It was at some point taken over by Merlin Satanspawn. After he died he was buried beneath the bar and placed a curse on his descendents; one of them would always have to look after the bar, and they couldn't leave until another descendant took over.
The current owner of the bar is Alex Morrisey and he is no longer compelled to stay at bar since Lilith killed Merlin. It is a very old and not the cleanest place, people come there to drink and brood.
The bar has very old protections and Merlin added to them with his magic, but how much remains after his death is unknown. The cellars under bar are protoected even more, due to Alex´s ancesters buried there.
Although it is interesting to note that the denizens of the Nightside still respect the neutrality of Strangefellows; maybe there are still protections and awful magics left protecting the oldest bar in the world.
Most informations about bar contains book 5 in the Nightside series, The Paths Not Taken. That includes names for the bar. However in book 11 A Hard Day´s Knight, John doesn´t know, that bar was named Avalon and Kay (king Arthur´s brother) says that the Avalon was nonsense name he created. It hard to say if it was author´s error or intent.