According to this interview with Peter David (who wrote the episode "Soul Mates", originally entitled "Pestilence, Famine and Death"):
"Daggair was Pestilence. Timov was Famine. Mariel was Death."
"At first I was going to have all their names be reflections of the
titles "assigned" them by Londo, but I decided that would be too
cutesy. The only holdover from that idea is Timov, whose name
backwards is, of course, Vomit. (I'll never forget Jane Carr coming
over to me the fifth day of shooting and saying in that accented voice
of hers, "Peter...did you know that my character's name is vomit
spelled backwards?" Uhhhh...well, yeah...)"
"You all realize, of course, that Londo is--by process of elimination--