Because Gryffindor and Slytherin are rivals and Snape did not like Sirius' friend, James Potter. Also, Sirius and James targeted Severus as someone to humiliate throughout their school years.
Severus Snape and Sirius Black have been enemies since they were at Hogwarts. James Potter and Sirius were best friend, and since Snape detested James, he naturally hated Sirius, too. Several times they argue in "Order of the Phoneix" over Sirius's inability to help the order as much as the other members, since he is falsely believer to be a mass murderer. The two usually bicker pointlessly without any real point to their arguments.
When Hermione's opened her bag and told Harry where they were [The Forest of Dean] the portrait of Sirius's Godfather that was in her bag heard and told Severus Snape via his other portrait in Snape's office. Snape then went to the forest and sent his patronus which Harry followed.
Severus Snape
No, in fact, both of them hate each other.
In the movie, Severus Snape is seen sitting next Madam Irma Pince, the librarian of Hogwarts. On his other side is Professor Filius Flitwick.
J.K. Rowling has said that Severus Snape, along with many of her other characters, are loosely based on people she knew in real life, but developed their own distinct characteristics as she developed the character. Professor Snape is loosely based on a professor she had herself.
The main characters are Harry Potter, Ron Weasley, Hermione Granger, Albus Dumbledore and Lord Voldemort. Other important characters include: Severus Snape, Ginny Weasley, Neville Longbottom, Draco Malfoy, Minevra McGonagall, Bellatrix Lestrange, Remus Lupin and Sirius Black.
The same actor as the other movies Alan Rickman
James did not hate severus snape. James only want to pick on Snape. Snape liked lily Evans also known as Lily potter Well yes mostly because of Lily. Becaus James loved Lily but so did Snape. SO that just makes them hate each other. I hope your welcome. I loved your answer ^^ Plus1: Snape kept spying on them, because he wanted to know Lupin's secret. Plus2: According to Sirius, Snape adored Dark Magic, James hated it. Well what he did (tormented Snape with Sectumsepra and Levicorpus), could be very easily describe as Dark. And he was a rotten bully as a boy, cursed random children just for fun (also according to Sirius))
There are many reasons. James Potter and Severus Snape both loved the same person, Lily Evans. Lily hated James but was friends with Snape until her fifth year. She began to date James in her seventh year after he grew up a little. However, both were very jealous of each other. James also hated Snape because he was a Slytherin and supported the death eaters.
Cedric Diggory Sirius Black Albus Dumbledore Alaster "Mad-eye" Moody Dobby the Free House Elf Fred Weasley Nymphadora Tonks Remus Lupin Young Colin Creevy Severus Snape (he was spying on Voldemort for Dumbledore) Many other's died, although I am not totally sure who is good and who is bad. But these are the most good people.
severus snape was killed by voldemort voldemort was killed by harry potter molly weasley killed bellatrix lestrange severus snape killed dumbledore (dumbledore asked snape to kill him as he was dying anyway and so it wouldnt damage damage malfoys soul) fred weasley was killed, and so were lupin+tonks and many other in the great battle of hogwarts.