Robert Jordan seems a little older than Frederic Henry, he already is an instructor and came to Spain first in 1925, so he is about 30, Henry is still studying. The links to his grandfather who fought in the American Civil War as did Ernest Hall and Anson Hemingway, the author's own grandfathers, are deeper, but they are just memories, as his grandfather is already dead. He asks him for help and advice and thinks he was "the hell of a good soldier"(For Whom (5.), p. 360) who, being a leader of irregular cavalry, must have been in similar situations. He admires him for having endured four years of Civil War.
At the time of "For Whom the Bell Tolls" the author's mental wounds had healed enough to allow him to reflect upon his father's suicide. Of course, this reflection is executed by Robert Jordan, but the parallels simply can't be denied. Jordan's father shot himself with an old Civil War pistol, as did Clarence Edmonds Hemingway and Jordan's father did it to "avoid being tortured"(For Whom (5.), p. 70), a reference to Hemingway's father's incurable illnesses. Jordan understands it, but doesn't approve it. He refers to his father as "the other one"(For Whom (5.), p. 361) and considers him a "coward"(For Whom (5.), p. 361). Although he knows his father had become what he was because he was trapped between the famous grandfather whose deeds he could never surpass and his dominating wife, Robert still feels ashamed. He himself is not married, at least not by law or church, and has no brothers or sisters.
As Karkov put it, Robert Jordan is "a young American of slight political development but a great way with the Spaniards and a fine partizan record."(For Whom (5.), p. 454). He is no Communist or Marxist but "an anti-fascist"(For Whom (5.), p. 69), just like Hemingway. For the duration of the war, however, he is "under Communist discipline [...], because, in the conduct of the war, they were the only party whose program and whose discipline he could respect."(For Whom (5.), p. 175). He is embarrassed by phrases like "enemies of the people"(For Whom (5.), p. 176) and other communist clichés, dialectics and a "purely materialistic conception of society"(For Whom (5.), p. 324).
He has the intention to write a book about Spain and the Spanish Civil War, Karkov, much admired and respected by Jordan, aids him because he thinks Jordan writes "absolutely truly"(For Whom (5.), p. 265), like Hemingway did, or at least claimed to do. He considers writing a way to get rid of all the experiences worrying him now. Interestingly enough, he thinks the book will be "Much better than the other"(For Whom (5.), p. 178), most likely referring to "A Farewell to Arms". In spite of having written the book in a third person selective omniscient perspective, Hemingway wants to be identified with Robert Jordan.
Robert Jordan is not as straight as Frederic Henry. Not only does he show a more differential way of thinking, but also he is inclined to talk to himself, especially in the second half of the novel(For Whom (5.), p. 323)
But you like the people of Navarra better than those of any other part of Spain. Yes. And you kill them. Yes. [...] Don't you know it's wrong to kill? Yes. But you do it? Yes.
He even insults himself sometimes reminding the reader of the argument between Anselmo and Pablo at the start of the novel.(For Whom (5.), p. 13)
"Art thou a brute? Yes. Art thou a beast? Yes, many times. Hast thou a brain? Nay. None."
Naturally, his attitude towards violence is different from Henry's. He believes it is justified to kill people for the cause, though he does not enjoy it. He is convinced that a victory is the only acceptable solution to this conflict. Their different attitudes result from their different motivations: Henry is just on some kind of adventure holiday while Jordan defends the country he "would rather have been born in"(For Whom (5.), p. 16)
Because of the gravity of the situation and the importance of his work, he can't permit himself emotions and feelings, he considers them as being luxuries, so he tries to restrain them, but is not always successful in the beginning, it takes him quite a while to extinguish them. (322-323)
One of the central aspects of the novel is Robert Jordan's education. In the beginning, Robert Jordan's world is a very simple one, he has got a task and he has got to accomplish it, no matter how high the cost. He knows "it was wrong in the first place and such things accentuate disaster as a snowball rolls up wet snow"(For Whom (5.), p. 413), but "he did not give any importance to what happened to himself"(For Whom (5.), p. 4). When he gets to know the people of Pablo, he fears his orders could harm or even kill them. The responsibility for the ones he likes is hard to bear, and when he fell for Maria, he "would abandon a hero's or a martyr's end gladly"(For Whom (5.), p. 177). At first, he considers this development a corruption of his fighting spirit, but later asks himself: " [...] was it corruption or was it merely that you lost the naïveté that you started with?"(For Whom (5.), p. 255). Especially Pilar became his mentor ("All right, Inglés . Learn. That's the thing. Learn."(For Whom (5.), p. 272)), a trait she could have derived from Hemingway's mentor Gertrude Stein. He learns to value his own life and to enjoy it, even though it's overshadowed by his forthcoming death and when it's over, he hates to leave it all behind.
Much of his education consisted of looking behind the scenes of the party propaganda. When he heard about the execution of the fascists in Pilar's home village, he is startled. To discover that the Loyalists can be brutal, too, is just the first part of the disclosure slowly emerging on his mind. The other part is the discovery that the dreaded fascist soldiers he is fighting and killing are simple peasants like the Republicans. On page 176, Robert thinks that all Spaniards are equal, just their leaders betray and abuse them, but every time he realizes this, he manages to suppress it, like Frederic Henry, because it would otherwise damage his resolution.
Apart from the obvious effects of violence on his development, the prospect of an early death influences him greatly. The knowledge that he has got to live his entire life in just four days acts as a catalyst for his development and made it possible in the first place.
Robert may seem to be the perfect continuation of Frederic Henry, but "For Whom the Bell Tolls" is more than a mere "A Farewell to Arms Part Two". Undoubtedly, the protagonist is the same, but there are those little differences that are already explained above, and apart from them, the major change is the introduction of two more main characters: Pablo and Pilar.
With Hemingway, it's always useful to try and associate the fictional characters with the ones of his real life. Since the protagonist's identity is well known, it's sound to associate Jordan's beloved Maria with Hemingway's beloved Martha to whom the novel is dedicated. The phonetic similarities in their forenames support this association. Pilar could correspond to Pauline Pfeiffer, since "Pilar" was Pauline's secret codename when Ernest was still married with Hadley. Pablo is, in an informal way, the husband of Pilar and they knew each other for quite a while, like Pauline and Ernest did. They behave like a long-married couple, so maybe Pablo is the personification of an Ernest who hadn't made a clear break with Pauline. Maybe he identifies with Pablo, a useless drunkard most of the time, but when things are getting serious, he shows grace under pressure and acts according to the "No man is an Illand" theme right from the start ("my duty is to those who are with me"(For Whom (5.), p. 16)). Robert Jordan does not value this theme right from the beginning, but seems, with his firm beliefs and his whole life still ahead of him, to be the best possible development Frederic could have had, while Pablo, with the alcoholic sentimentality of a man who knows his best years have already passed, represents the worst possibility. The reality, i.e. the author himself, struggles somewhere in between. On the one hand, he tries to stay away from Pablo, whose enthusiasm and resolution vanished a long time ago, who doesn't care much about politics and who definitely is unwilling to die for the cause, no matter how important it might seem. But on the other hand, he can't be like Robert Jordan, whose single-minded illusions about the strength of their enemies, about the possibility of a victory, about sacrifice, and about the justness of the cause appear very naïve.
Pablo is what Ernest fears to become and Jordan is what he once was, so the conflict between them could represent Hemingway's struggle with his former self, which is displayed best by Frederic Henry. As observer of this conflict acts Pilar who likes Robert, because he is formed out of the author's early characteristics. She is concerned about the first signs of assimilation Robert already shows, she warns Maria: "You are going to have a drunkard like I have"(For Whom (5.), p. 70).
What Hemingway tries is to get the best out of both characters, maybe to develop a guideline for his own life. They adopt each other's virtues and are able to drop some of their flaws. Robert gets, mostly via Pilar, some of Pablo's experience and is able to obtain a certain degree of wisdom, while Pablo is forced out of his "stagnation that is repugnant"(For Whom (5.), p. 33) and gets some reaffirmation of his spirit and resolution.
In spite of that, the differences are still huge and although Robert considers Pablo a smart man he strictly disapproves his brutality and low cunning. Pablo improved a little at the very end of the novel, but Robert still is by far the most virtuous character. If seen under this aspect, the novel's end appears more tragic than it did before, because it is also the end of Hemingway's inner struggle with his Lost Generation ego, that gives in to the drunken cynicism of Pablo, in whom Hemingway implies, deliberately or not, visions of his own future and facts of his present. It is not only the fictional character Robert who dies, but also the part of Hemingway's mind that he represented. He stopped fighting his latent depressions, his alcoholism and his brutality and was slowly overwhelmed by them.