I've been following a story from 3.5e to 4e related to Nerull... but in 4e he does not exist! :o what happened to him in 4e?
Nerull trapped and tormented souls in Pluton (a domain of the Astral Sea in the Points of Light setting), plotting to become the king of the gods... until his mortal consort killed him and acquired his portfolio.
She's now known as the Raven Queen. However, due to... reasons... the gods withheld her authority over the dead, so her powers are focused on death itself.
More details can be found in Divine Power and Manual of the Planes.