Vice Admiral James Greer (Ret.) is the CIA Deputy Director of Intelligence and personally recruited both John Clark and Jack Ryan into the CIA.
In several of the Jack Ryan novels (notably The Hunt for Red October and Patriot Games) Greer was the Deputy Director of Intelligence in the CIA. He had a taste for coffee, and was never seen without a cup of it, having a coffee machine in his office.
Greer dies from pancreatic cancer during Clear and Present Danger and is laid to rest next to his only son, First Lieutenant Robert White Greer (USMC), who died in Vietnam.
In the novels, Patriot Games was a prequel to The Hunt for Red October; however, the chronology of the movies was altered for The Sum of All Fears. While the novel takes place after Clear and Present Danger, the film takes place earlier in Ryan's career and how he met Greer.
The Sum of All Fears was not part of the Alec Baldwin/Harrison Ford trilogy, but rather an intended reboot of the franchise. The discrepancy can be seen in the fact that he met John Clark for the first time in Clear and Present Danger and the Clark character was significantly different; Ryan is also married in the first three films. Greer didn't appear in the film, with the exception of William Cabot, a fusion of Greer and his successor Marcus Cabot.
In 2018, a new Amazon Original series, titled Tom Clancy's Jack Ryan, sees actor Wendell Pierce in the role of Adm. Greer.