Pretty Little Liars hasn't been kind to the women of Rosewood. Across seven long, tumultuous seasons, the diabolical A has dragged the Liars — and everyone else in their life — through cruel, relentless torture, passing the baton from one villain to the next like a demented game of telephone. Ironically, the one who started it all has also been put through some of the most: Pretty Little Liars' own Mona Vanderwaal, the original A turned Liar ally (at least, for now). At first, it may have seemed that she played only a peripheral part in Alison and her cohorts' story, but, as the show pressed on, something began to shift, and Mona quietly became the most important character in the series.
Her significance is twofold. In relation to the plot, Mona has been one of PLL's only consistent driving forces. She's had a stake in the A game since its inception: First, as its creator, and later, as a victim. In fact, if it weren't for her, it's more than likely that the Liars would never have been subject to so much anguish in the first place. When Mona did finally step out of the darkness and onto the Liars' side, she committed herself to atoning for her past transgressions, and has since saved the women on more than one occasion. Without her, they'd arguably have been caught by A — or the police — long ago.
But on a deeper, more affecting level, Mona is also the one who's done the most growing. When she was first introduced on PLL, she was vain, callous, and domineering — a person not unlike the one who'd made her life a living hell. She'd managed to find her voice and finally stand up for herself, but not without becoming someone the true Mona would have hated. And the same applied to her revenge scheme. In wanting to reclaim her own strength, she tore down the lives of others — including her own best friend.
But while Hannah, Emily, Aria, and Spencer still tend to fall back on their old faults, Mona seems to have genuinely learned from her mistakes. She's proven herself a steadfast ally for the Liars, and yet they continuously shut her out, despite the fact she's weathered her own fair share of trauma. Instead, she's PLL's perennial outcast — indefinitely relegated to the sidelines, when all she's ever wanted is acceptance.
The Liars are, of course, understandably wary of Mona's intentions, but if almost going to prison for Hannah's mom and helping them cover up a murder didn't earn their forgiveness, it's tough to imagine what will. And even still, Mona continues to stand by them.
More recent PLL episodes have hinted that Mona may have returned to her devious tendencies, but for a show that prides itself on unprecedented curve balls, it seems an obvious red herring, which means that she's actually hot on the trail of Uber A. If things continue down the same road, she won't be the ultimate big bad, but rather the show's crowning hero, and perhaps, finally, she'll have earned her saving grace. It would be the perfect finale: Mona started the A game, so it's only fair that she ends it.