You guys know what Greasers are? White trash with long greasy hair.
~ Bob Sheldon
Robert "Bob" Sheldon is a major antagonist in S.E. Hinton's 1967 novel The Outsiders, and its 1983 film adaptation of the same name. He was the leader/one of the leaders of the Socs until he was killed by Johnny after trying to drown Ponyboy in a fountain.
Bob has dark brown curly hair. Like all Socs, he wears dress pants with a button-up shirt and button-up Jacket. He also has a Mustang like most Socs meaning he prided himself in his good looks and cars.
Bob expresses a hatred for Greasers, especially for since he was a Soc leader. Whether this is out conformity or a personal reason is unknown; however, he did hate Johnny and Ponyboy even more after they along with Two-Bit, tried to take Cherry and Marica home as he suspected that they were trying to take them away. He shows no remorse for the way he treats them even stating to Ponyboy that he and his friends were going to beat him up why did they before. He also shows that he is sexist by treating Cherry more as an object than anything.
In the movie version, his treatment of her becomes even worse as he tried to kiss her without permission at one point. Despite this, one might argue that he reasons he acts this way was beccause of his parents neglecting him and never making him work for anything. Both Cherry and Randy conform this. Cherry while explaining to Ponyboy that Bob had his "moments of being sweet" indicating that he was much nicer when he wasn't drunk or at least loyal to his fellow Socs. Randy, meanwhile, outright states that he would have been alive if his parents showed him some tough love every once in a while. This makes Bob a tragic yet still selfish young man who would do anything to make himself feel better. Even if it meant killing those who messed with him. Because of this, Ponyboy eventually realized that Bob along with the other Socs, were still humans with feelings, and in Bob's case, similar traits with the Greasers.
Bob pulls up with his friends, including Randy Adderson, in his Mustang. He and his friends are infuriated to discover that Greasers Ponyboy, Johnny, and Two-Bit have befriended their Girlfriends, Cherry and Marcia. The girls defuse the situation by going with the Socs. The movie also shows why the girls left in more detail as the boys were clearly drunk with Bob also showing a lack of respect towards Cherry while in the parking lot.
Bob pulls up to the park, seeing that Ponyboy and Johnny are alone at an hour where other Greasers wouldn't be around to help them. Bob comments to them to them that Greasers are nothing more than white trash. In retaliation, Ponyboy calls Socs white trash with Mustangs and other nice things. Bob and his friends then chase down the two and start to drown Ponyboy. it takes all five of them to keep him down. Because of this, Johnny was able to get his knife out. Johnny then stabs and kills Bob Sheldon. It isn't known if Johnny intentionally meant to kill Bob or not. However, given that Bob was the one who ordered the attempted murder on Ponyboy and scarred Johnny for life, it's possible that Johnny stabbed him on purpose.