Like the rest of her siblings, Delirium is neither a mortal being or a god, she is the personification of delirium (or madness) itself. Her realm is almost completely formless, containing colors, shapes, feelings, smells, thoughts, that mingle freely and without cause. Even she can become lost in it. At it’s center is a sundial with an inscription in Latin translated “Tempus Frangit” (Time Shatters, a pun based on "Tempus Fugit" or Time Flies) on it. Her sigil is a chaotic pattern. 

She is one of the most regular of recurring characters throughout the series. It often spoken of that long, long ago, perhaps millions of years, she was once Delight, but why or when that change occurred is not known. Her appearance changes frequently with the only constant being that one of her eyes is blue while the other is green. Even her shadow never reflects her shape, and is tangible, like velvet. She speaks of random topics and it is hard to get her to follow a thread of any conversation. Her childlike appearance and nature makes her seem an innocent, but she is far from it, visiting mortals in their worst moments of madness.

She is closest to Death and Destruction, because they are fond of her and protective, but Delirium finds Dream (Morpheus) "scary".

Wanting to find her prodigal brother Destruction. She first attempted to convince Desire and Despair to help her, but they refused. She then turned to Dream help her look for destruction through Destruction’s old friends such as Ishatar, the Goddess of Love and War. (Eventually, this journey would taken them to Dream's son Orpheus, who was the "only Oracle who could tell them of their family", thus setting in motion the events of Morpheus downfall.) During an encounter with their eldest brother Destiny, Delirium revealed that she knew why her transformation from Delight into Delirium took place even when Destiny did not and that if necessary, she could pull herself together for short periods to speak with clarity and purpose.

When Destruction left, he hinted the Delirium would go through yet another transformation. He left her with his companion, a German Shepherd dog named Barnabas.

Delirium knows pathways outside of Destiny's garden, which only she may travel.