Published November 17, 2014
The retired general's family announced his death Saturday in a statement, without giving details. Muller had health problems for years, which had worsened recently.
Chavez mourned Muller's death on Twitter and expressed his admiration for a colleague who for many years was a prominent ideologue in the president's socialist movement.
In March, Muller had left the party saying he was disillusioned with the direction of the "revolutionary process."
Muller retired from active military duty in 1985, and in the following years was a governor and senator.
He was Chavez's campaign manager for his first elected in 1998 and was seen, especially in the early years of the administration, as an ideologically committed adviser who had Chavez's ear.
In 2005, Chavez brought Muller back into the army to join a group of senior officers working with the president's office.
Muller and Chavez appeared to maintain an affection for each other in recent years even as the former general had differences with Chavez and his party. Chavez has said he valued Muller's criticism.
When the president removed Muller from his post as a military adviser in 2007, Muller said he was sure it was under pressure from crooked generals who wanted him out.
The two later smoothed over that episode and Muller became active as a vice president of Chavez's socialist party.
When he left the party in March, he said in an interview with the Venezuelan newspaper Panorama that "it's rare that the president listens to me."