The relationship between the cured vampire doppelgänger, Stefan Salvatore and the tribrid doppelgänger, Alexandria Gilbert, is a complicated, but a popular and powerful romantic pairing, and a significant relationship in the series.
Stefan and Alex were the original and main couple of the series. Stefan originally returned to town to get to know Alex after saving her and Elena from a car accident. They instantly fell in love and began a romantic relationship in Season 1. At the end of Season 2, they've come strained when they leave together with Klaus. Throughout Season 3 they've tried not to make it awkward while they spent the summer together with Klaus. They both agreed they should break up cause they both couldn't be in that kind of relationship with Klaus always there. She admitted to Stefan that she and Klaus kissed in the middle of Season 3. In Season 4, she was off and on again between Klaus and Stefan, not being able to choose one or the other. At the end of Season 4, she and Stefan officially ended things as she left for New Orleans to have the summer of her life: only to find out she was pregnant with Klaus' child. In Season 6, she returns to Mystic Falls to be their for Caroline as her mother had died. Stefan tried to rekindle their love but she states that she had to marry someone to set her people free. He tells her that he'll wait for her forever. In Season 8, they rekindled their relationship and had triplets. At the end of season 8 he becomes human and sacrificed his life to save Mystic Falls from Dark Alex.
They are referred to as "Stalex" by fans.