Short answers, pulled from the story.
Tom Veitch and Cam Kennedy developed the Dark Empire story for Marvel Comics in the late 1980s. The initial six-issue limited series began publication bimonthly in 1991 and concluded in 1992.
Emperor Palpatine survives death by transferring his spirit into successive cloned vessels housed within a fresh body on Byss. He attempts to possess the infant Anakin Solo but is blocked by Empatojayos Brand who sends his soul into darkness to prevent return.
The first six-issue limited series ran from 1991 to 1992 followed by a second six-issue series from 1994 to 1995. A final two-part conclusion arrived in 1995 before sales figures exceeded one hundred thousand copies printed by the end of the decade.
Disney acquired Lucasfilm in 2012 leading to a reclassification of most licensed material as non-canonical Legends. In April 2014 Lucasfilm branded these stories as separate from the main continuity while The Rise of Skywalker film utilized the plot element of Palpatine returning via cloning.