"We cannot say Ri is not a hard-liner, but Kim Kyok Sik has a reputation for taking an extraordinarily hard line on South Korea," said Cheong Seong-chang, a senior fellow at the private Sejong Institute in South Korea.
He said it "would be burdensome" for North Korea to keep Kim in charge of the army when it was trying to improve ties with the outside world.
Kim Jong Un has frequently replaced top government, ruling party and military officials since taking power following the December 2011 death of his father. Analysts say he wants to install new figures loyal to him in key posts. Ri is Kim's fourth general staff chief in less than two years.
"The fact that he can frequently replace the top army officer shows he has a firm control over the military," said Koh Yu-hwan, a professor of North Korean studies at Seoul's Dongguk University.
One of the most notable personnel changes Kim oversaw was the firing of military chief Ri Yong Ho, who was once dubbed as Kim's mentor. State media said he was dismissed in July 2012 due to an unspecified illness but analysts speculated Ri was purged as Kim was trying to reshape the government.
Nearly half of about 220 top government, Workers' Party and military officials have been replaced since Kim took power, according to Seoul's Unification Ministry.
On Thursday, North Korea marked the 68th anniversary of the founding of the Workers' Party, with leader Kim paying respect to his late father and grandfather at the Kumsusan Palace of the Sun in Pyongyang.
South Korea, the U.S. and Japan on Thursday began two days of naval drills aimed at improving readiness for maritime disasters. Pyongyang earlier called the drills a military confrontation and said its troop were ready to repel any enemy provocation.
