The antagonistic relationship is between the cured vampire/human doppelgänger, Stefan Salvatore and the vampire, Julian. Stefan originally wanted to kill him right away, opposite from what his brother wanted. However, after Stefan told Damon what Julian did to him and Valerie, Damon was in on the plan to kill Julian right away and be done with him. After struggling to do so, Stefan finally got the opportunity to kill Julian. Both Stefan and Valerie fulfilled their desire to kill Julian for being responsible for Valerie's miscarriage.
Stefan meet Valerie and Julian in 1863, at the County Fair in Mystic Falls. Unknown to Stefan -who is still human at the time- Valerie is a Siphoner and Julian is a Vampire, who per his mother's orders, came to Mystic Falls to make sure Stefan was doing well before they left for Europe. When Julian notices the developing relationship between Stefan and Valerie, he attempts to separate them, but Valerie uses a cloaking spell, fueled by the magic within an amulet intended for emergencies, to hide her and Stefan, allowing them to leave the fair and go into the woods to make love. That night, Julian tracks them down at Lily's grave, expecting Stefan would visit there at some point. Julian angrily takes Valerie away, reminding both of them that the two of them are leaving for New York.
On the day they are preparing to leave New York Harbor for Europe, Julian catches Valerie sneaking away with a view to reunite with Stefan as per her promise to him. When Julian finds out that Valerie is pregnant with Stefan's child, he beats her senseless until he kills the unborn child inside of her in the process and nearly kills her.
Stefan didn't know about that until 150 years later.
Throughout The Vampire Diaries Series
In Age of Innocence, a flashback shows how Stefan met Julian in 1863, at the County Fair in Mystic Falls.
In Live Through This, Valerie seeks Stefan's help to find Julian and help her kill him. Later he discovers that Julian is dead and his body is hidden. After finding the location of Julian's body Valerie attempts to kill him permanently by buying his body in front of Stefan. But unfortunately Stefan's mother Lily and her heretics save Julian from Valerie and later resurrect him. When Stefan asks Valerie the reason of her hatred towards Julian, she reveals to him that she was pregnant with Stefan's child and Julian was the person who killed their child before he was born. Stefan then promises Valerie that he would take revenge on Julian by killing him himself.
In Best Served Cold, Julian discovers that Lily's sons Stefan and Damon are alive. Lily tries to introduce her sons to Julian by throwing a welcome back party for Julian. Stefan attends the party with a view to kill Julian. In the party Julian meets Stefan for the first time in modern time. Stefan attempts to kill Julian while playing pool but is interrupted by Damon who thinks Stefan is out-matched by a vampire like Julian who is at least three hundred years older than him. Shortly after, Stefan again attempts to kill Julian by throwing him into the fireplace. Julian gets saved by Lily. Damon also joins them. Julian, being older than Damon and Stefan combined, brutally beat them into submission, nearly killing them before being stopped by Lily. Stefan later reveals to Damon that Julian killed his unborn child with Valerie to which Damon agrees to help him take down Julian. Seeing the brutal nature of Julian, Stefan expresses to Damon that he reminds him of their father the mighty Giuseppe Salvatore.
In Mommie Dearest, Stefan informs Lily that Julian killed his unborn child who at first doesn't believe but eventually realizes that he is right.
In Cold as Ice, Stefan along with Damon tracks down Julian with the help of Bonnie, who is on a killing spree because of the death of his love, Lily. As Julian comes with few of his companions, Damon manages to take away Stefan as they are out numbered who is still hellbent on killing Julian. To draw Julian out, Stefan takes Mary Louise hostage, texting Julian to meet him at the Salvatore House. Julian then goes to the house and discovers Damon, who isn't aware of Stefan's plan. Stefan arrives and attacks Julian but Julian once again overpowers the brothers, stabbing Damon with the Phoenix Stone sword.
- Julian is at least 300 years older than Stefan.
- Julian killed Stefan's child before it was born.
- In Best Served Cold, Julian finds out that Lily's son Stefan is still alive.
- To draw Julian out, Stefan kidnaps Mary Louise.