That is what Vincent tells Mary about Santino when she asks, but in fact Vincent had to have been a baby when his father was murdered.

We all know that Sonny was hardly the "prince of the city (with apologies to a film of the same name, unrelated to the GF)." He happened to be the eldest son of a respected and at the time long gone Don. In reality he was the reason Barz and the other families gave Sol the green light to take Vito out. They knew he was "hot" for the idea of the drug trade by virtue of his blunder at the meeting. They also knew he ha a terrible temper, was a philanderer, and was not at all the man Vito was. To me he was a train wreck waiting to happen, and but for the ascension of Michael, he would probably have ruined the family. Besides, he didn't even live in the city when he was single, he lived in the compound until he got married and had a small apartment.

So where does this come from? At first I thought Vincent was glamorizing the family for Mary, but on further reflection it is probably what he had been told all of his life by his mother. She saw Sonny as an unobtainable "prince," who she probably believed died a hero trying to save his sister, instead of a hot head who went racing into the city on his own. All his life Vincent probably was taught to idolize his father, and thats why he said what he said.

It was not until Michael gently told him to watch his temper, that bad temper clouds judgment, and that bad temper did his father in did he possibly see Sonnny as the flawed Don he really was.

Actually,Sonny died before Vincent was born,so he really didn't have anything but the mythology to go on. From the script:

MARY
What was Sonny like?
VINCENT
He was the Prince of the city. Yeah -- he died before I was born but I heard a million stories about him, he was a legend.

Vincent also tells Mary that her father was a hero and that "he saved the Family".
In Vince's world,regardless of the truth,Sonny and Uncle Mike could do no wrong.
As we see,Vincent was not much more than an undisciplined thug when he got into the mix,so he wouldn't have understood or appreciated the nuances of the Corleones in the context of the Mafia as a whole.
As time went on,he was schooled by Mike,and really came a long way toward becoming a decent Boss.
However in his mind,all of the negatives that you correctly pointed out concerning Sonny would have been selling points for a young cugine like Mancini.

Vincent was a wannabee--a nobody who tried to cash in on his bloodline to get ahead because he couldn't on his own. So, it was in his interest to glamorize his never-seen father, and to be worshipful around his uncle (notice how he calls him "Mr. Corleone" at first when Connie brings him to Michael). Sure, Vincent heard a million stories about his father, and probably some of them touched on the negative points that dt raised in his post. But, to Vincent, his father had to be "the prince of the city."

Actually TB, if you listen closely, what Vincent says is "He pranced around the city."

Im not sure how Vincent was a wannabee. He was young but he was still a gangster, By the end of Part 3 he was very capable

You have to give Vincent credit for the hit on Joey Zasa. He organized the hit without the help of Michael and carried it out perfectly, even when it was believed to be an impossible task. By doing so he made his bones the same way Vito did when he killed Fanucci and established himself as 'a man of respect'. When it comes down to it this is how your capabilities are measured in the Mafia and Vincent had effectively shown to be a skillful organizer and capable leader.

...thanks to Michael's tutelege...

I never disputed that

Vincent was not a wannabe, but he did desire "legitimacy" within the family (as Michael wanted "legitimacy" in the world). It is no accident that after Michael made him apologize to Zasa that he stuck around to tell Michael that he knew Zasa was angry because Michael was keeping him from rising up in the commission. He also took full advantage of Connie's desire to see him succeed Michael, and he even had the affair with the none too attrative Mary.

Basically Vincent came from nothing and becoming a real member of the Corleone family was the culmination of his mother's and his lifelong desires.

That said he didn't do such a hot job securing things at the Opera. Maybe he was on Altobello's payroll.

Another good point, dt.
It looked as if Vincent had manipulated Michael: he buttered up Connie ("how's my favorite aunt?"), inveigled a meeting with Michael, tried to scare him with tales of Zasa's treachery, and reassured him that he'd take care of it.

Fool! Did Vincent think he could manipulate Michael Corleone, the Master Manipulator? Instead of falling in with Vincent, Michael, in a completely calculated move, threw him to the wolves--calling him "foolish" for not accepting Michael's offer in the "legitimate world," praising Zasa's "good heart," and demanding that he make "peace" with him. Had Vincent gone along, Zasa would have killed him--with Michael's permission. Michael wouldn't have let that happen because letting Zasa get away with whacking a blood relation would have depositioned him.

So, he put Vincent right up against the wall, and Vincent declared war on Zasa by biting his ear. But Michael won. In effect, he told Vincent, "you can't just buzz in and out of my life whenever it pleases you. Now you really owe me. You need to go with me now to save your life." At the same time, the entire incident warned Michael that he couldn't ignore Zasa--and he needed a willing killer like Vincent to protect him. Vincent would become his new Neri. Michael was brilliant.

Yeah, but so was Vincent because he accomplished what he wanted... he got his foot in the door.
Interesting, at the end of the day he ends up a tragic figure as well.

His whole life was predicated on the glory of the Corleone family and his desire to be a major player in it. Just when he achieves his dream, he loses the love of his life (through Michael's cunning and an assassin's bullet) and he loses whatever power he had. After Mary's death Michael was finished, and Vincent reigned over nothing. You think Neri stuck around to help him? Not in a million years.

If there was anything left of the Corleone's businesses,I wouldn't be surprised to see Neri kill Vincent and take over. But I think that by the end of the trilogy,we saw the last of the Family,and Neri would probably just go on his own. I don't think Al respected Mancini or even considered him a "real" Corleone,despite his public acceptance of Vincent as the new Don.

Yeah, Neri probably had enough money from his years with Michael to get himself a place in Vegas and another place in Sicily to retire. My guess is Neri died of old age in bed.

Actually despite Mary being killed Vincent was still teh ehad of the corleone crime family. he took over what zasa had so he was quite powerful. According to Coppola Vincent continued to be boss of the family until his eventual death similar to pablo escobar's fall

Ya apperently the plan was that vincent was gonna turn the family into a drug cartel. Then vincents death(not micheals) would mark the end of the corleone family.

Mafia bosses give themselves up peacefully to law enforcement, so not realistic. There should never have been a GF III, never mind a IV.

I read the Godfather novel recently for the first time after seeing he films hundreds of times. What proof do we have that Vincent is sonny's son. I mean they have his mom moving to Vegas after his death and messing around with the doctor and when he gives her the surgery on her sex organ he ask her is she pregnant and she replies no. So I'm kind of confused here!

None.

The bastard child is a creation of the films. It is not mentioned in the novel.

As someone posted here several years ago, considering how much Puzo talks about Lucy's vagina, he certainly would have mentioned it had a baby come out of it.

Vincent is just FFC inventing something to make GFIII more compelling.

If Puzo is to be believed Vincent could have driven out.

There was a lot to like about Sonny--he'd be great to have as a brother, he clearly loved his family deeply, and he was very passionate (in more ways than one). Of course, people's strengths and weaknesses are often two sides of the same coin, and the obverse side of his passion was his hotheadedness. Still, if I were Vincent I'd be proud of him too.