Who is Manuel Ruiz from The Tears of Autumn and what is their importance?

Manuel Ruiz is a Cuban Marxist, protégé of Ché Guevara, Ruiz uses a variety of surnames including Rogales and Linares, but always with Manuel as the given name. He is a great jungle fighter, surveying revolutionary prospects for Guevara in Bolivia, Columbia, and Panama. He disappears in August-October 1963 in North Vietnam during the planning of John F. Kennedy's assassination. Ruiz recruits Lee Harvey Oswald in Mexico City after New Orleans Cubans vet Oswald and reject him. Ruiz doubts that Oswald will succeed, despite Do Minh Kha's absolute confidence in the horoscopes.