Who is Harry's character foil in Harry Potter and the Sorcerer's Stone?

In J. K. Rowling's Harry Potter series, Draco Malfoy is a clear foil for Harry. From the very beginning of the first novel, we see stark contrasts between Draco and Harry. When Harry first goes to Diagon Alley with Hagrid, Draco is in Madam Malkin's with his mother. Harry, on the other hand, is not there with his parents, because he is an orphan. We immediately get the impression that Draco is a spoiled brat and snobby, whereas Harry has essentially been emotionally abused his entire life and has no sense of entitlement (at least this early in the series) whatsoever.
Draco also makes comments about how he knows he will be a Slytherin:

Well, no one really knows until they get there, do they, but I know I'll be in Slytherin, all our family have been—imagine being in Hufflepuff, I think I'd leave, wouldn't you?

Since Draco does wind up in Slytherin and Harry is sorted into Gryffindor, their houses place them in opposition to each other; in many ways, the houses of Slytherin and Gryffindor are foils to one another as well. The houses share the same qualities of resourcefulness and determination, but their members generally have very different moral beliefs and ideas about right and wrong.
Once the students arrive at Hogwarts, Draco becomes even more of a foil to Harry. Once he realizes who Harry is, Draco says, "You don't want to go making friends with the wrong sort. I can help you there," to which Harry coolly replies, "I think I can tell the wrong sort for myself, thanks." Draco is directly saying that Ron Weasley (who winds up being one of Harry's best friends) is unfitting as a friend for the famous Harry Potter.
We later learn that the Malfoys call the Weasleys "blood traitors" and constantly belittle them for not being wealthy and for associating with Muggles and other "undesirable" people. Malfoy's hatred of "mudbloods" is another stark contrast with Harry, since Hermione, who is Muggle-born, winds up becoming Harry's other best friend.
As time goes on, we see more and more of the characters of both Draco and Harry. For example, in the situation that erupts over Neville's Remembrall, Draco is cruel, while Harry is empathetic and friendly. Neville had just injured himself after falling from his broom in flying practice, and Draco snatches his Remembrall, which was left on the ground. Harry, who at this point does not know he can fly, chases Malfoy down by flying to retrieve it—even though Madam Hooch threatened expulsion for anyone she caught flying while she was gone to the hospital wing. Again, they both have a "certain disregard for rules" but are guided by very different moral compasses.
In the end, by seeing how horrible Draco is on a consistent basis in Harry Potter and the Sorcerer's Stone, readers can appreciate Harry's kindness, generosity, and humility all the more.
https://www.wizardingworld.com/writing-by-jk-rowling/draco-malfoy