When James learned what Sirius did, he stopped Snape before he reached the Shrieking Shack, saving his life. Snape, however, had seen Lupin in werewolf form and was sworn to secrecy by Dumbledore.
Snape hears Lupin admit this while hiding under the Invisibility Cloak and also hears Lupin explain that he was not part of Sirius's joke. Snape still thinks Lupin is helping Sirius, however, and attacks Lupin. He then lets slip that Lupin is a werewolf the next morning.
Snape thought Sirius wanted to murder Harry. Snape thought Lupin was helping Sirius to sneak into Hogwarts and then yes murder Harry. So of course Snape wanted Lupin out the castle, based on the information he had he believed he was saving Harry's life.
During their fifth year sometime before the Ordinary Wizarding Level Examinations.
Snape was aware that Lupin was a werewolf since they were students at Hogwarts.
According to Sirius, Lupin did not participate in his and James' bullying (of Snape, in particular), but Lupin regrets never having told them to stop. He is also one of the co-creators of the Marauder's Map, which later falls into Harry Potter's ownership.
Snape's rather complicated in certain respects. He really doesn't like Remus. But given Lupin's conversation with Harry during The Half Blood Prince we can conclude they came to something of a truce.
Yes, Dumbledore knew that Lupin was a werewolf. Due to his knowledge of Remus' lycanthropy condition, Albus Dumbledore even visited him personally to invite him to Hogwarts a Defence Against the Dark Arts teacher. Dumbledore even arranged for Snape to make Lupin the Wolfsbane Potion every fortnight.
The potion was brewed for Remus Lupin by Severus Snape to enable him to work as a Professor at Hogwarts without endangering his students.
While in school together, Sirius once tricked Snape into almost entering the Shrieking Shack while Lupin was there, transformed into a werewolf. James realised the danger and stopped Snape, saving his life; this is the incident Dumbledore referred to at the end of the first book.
But Lupin was actually in despair, convinced that he could not run the risk of marrying and passing on his lycanthropy to a child. Tonks, convinced that Lupin would never spend time with her again, became desperately unhappy.
As a refresher, Lupin meets HRH at 12 Grimmauld place and offers to join them to complete their task that Dumbledore gave them. Harry accuses him of being a coward for wanting to leave his family. Lupin ends up attacking Harry and rushes off.
Lupin was awarded the Order of Merlin, First Class
He was the first werewolf to ever be given the award, and his tale helped to lift the stigma surrounding the condition, which previously left werewolves cast out by their fellow wizards.
Hermione shrieks at Lupin that he is a traitor, and that she should have exposed him as a werewolf long ago. She says that she deduced his nature as a werewolf from seeing his Boggart turn into the moon, and from noting that he was out sick during each month's full moon.
Pour the memory of Snape's story into your pensive and you'll also notice he was already a Death Eater when he went to Dumbledore – Snape had joined up aged 20. And at just 20, he was already a skilled enough Occlumens to fool Lord Voldemort himself.
Lupin didn't appear to know, given his position in the discussion about trusting Snape. He could have been lying, but that's a bit of a leap. "It isn't our business to know," said Lupin unexpectedly.
To see his memories. Harry was later seen dropping Snape's tears into the Pensieve. Snape told him to. It was necessary for Harry to take his tears so that he would know what he needed to do to defeat voldemort.
Sectumsempra is a curse invented by Professor Severus Snape, during his childhood, when he was known as "The Half-Blood Prince". He created it with the intention of using it against his enemies, and it soon became one of his specialties.
Snape surely hates Wormtail as much as anyone. It's never really touched on much in the books, but Wormtail is just - if not more - responsible for Lily being killed as Snape is.
Bill is viciously mauled by the werewolf, Fenrir Greyback. Fortunately, as Fenrir was not transformed at the time, Bill did not become a werewolf, though Madam Pomfrey is unable to completely heal his face, and he remains permanently scarred.
On the night of 6 June, 1994, Remus Lupin stated that the Ministry "never knew that there used to be three unregistered Animagi running around Hogwarts", the three being his schoolmates Sirius Black, Peter Pettigrew and the late James Potter; Black's, Pettigrew's and Potter's Animagi nature was revealed by Remus Lupin ...
Did Dumbledore know the Marauders were unregistered animagi? No, he didn't until very much later. James, Sirius and Peter turned themselves into Animagi without the knowledge of the wise old headmaster.
Voldemort intentionally made six Horcruxes, but when he used Avada Kedavra on Harry, he unintentionally created a seventh Horcrux. Instead of dying, Lily's love for Harry created a counter 'curse' known as Sacrificial Protection and saved Harry.
In GoF, Sirius doesn't believe that Snape was a death eater. He says that he couldn't see Dumbledore allowing him to work at Hogwarts if he'd ever worked for Voldemort. But after Voldemort's resurrection, most people seem to know of Snape's status as a spy.
Voldemort trusts Snape because he's good at his job as a double spy and as an Occlumens. Voldemort is so conceited that he probably just doesn't expect Snape could be a better Occlumens than he is a Legilimens.