The former Secret Circle actress recently joined the cast of the CW's supernatural drama, playing a "wild, sexy and free-spirited" character named Hayley, who has a past with Tyler (Michael Trevino).
"I like that she's a world traveller, a bit of a tomboy, pretty ballsy and provocative, but not in the way Faye was on Secret Circle," Tonkin told The Insider.
"I mean, [Faye] went out to manipulate and see what she could gain from people. Hayley just doesn't have a filter. She didn't really have parental figures in her life, and I like that kind of a person.
"I like that she's tough and tries to keep up with the boys. That's what I responded to when Julie [Plec, executive producer] first pitched the character to me."
Tonkin will make her first appearance in the third episode of the show's fourth season, airing on October 25.
A series of character portraits have recently been released from the new season, as well as a clip from season premiere 'Growing Pains'.
The fourth season of The Vampire Diaries will premiere on The CW on October 11.
Watch series star Paul Wesley speaking to Digital Spy about the new season below: