There was a common fan theory that the Shadow Triad (a ninja-like group loyal to the leader of Team Plasma, Ghetsis, because he saved their lives as young children) in the games were actually the Striaton triplets.
The Pokemon Special/Adventures manga also hints this at first (making the Shadow Triads' masks even resemble the face markings of the elemental monkeys!), but eventually, all official Pokemon media reject the theory by making the Shadow Triad look either much older, stronger-built, give them different eye colours from the triplets, or have them battle them... the anime never explicitly denies a connection to Team Plasma simply because the Shadow Triad are absent entirely. The only manipulated children Ghetsis raises to serve him are N, Anthea, and Concordia, who broke away from him before the time of the anime's current story.
Still, the oddly frequent mask symbolism, Cilan's line about how a strong villain brings out the best in a hero/protagonist and enhances them (while Iris prefers heroines and ash prefers heroes), as well as his oddly Ghetsis-inspired villain costume in Luke's second movie (complete with Ghetsis' horn-like hair, staff, hidden eye[s]... they haven't met him yet!), and his fear of Purrloin make for interesting fodder for an old fan theory... if he's not a sleeper agent looking after Zekrom's hero of ideals (Ash), they possibly suggest some tie to Team Plasma, perhaps only as an innocent victim at some point!
Cilan has been depicted wearing masks several times during the series (including a masquerade mask, the mask of a Yamask that possessed him once, various masks while playing the villains in movies he helped Luke make, and even in baby Axew's dream where everyone‘s exaggerated, he sees Cilan with the same masquerade mask he wore to the party in the Plasma VS Rocket unaired two-parter (never aired due to the earthqake + Fukushima Daiichi disaster)...
He usually plays villains in Luke's movies and prefers villains to heroes, considering them the "main character[s] in the shadows" and liking how they bring out the best in the hero... when he had to ad-lib fo the first movie they woked together on due to Rocket interference, he restores his villain character to his "true self" a good and heroic character who aids the heroes!
In terms of what we know, Cilan is a good person. He was arrogant and mocking in the past, but quickly changed upon meeting Ash and learned not to be so quick to judge, althogh he was still a little too quick to bet Ash's team because he was so certain he would win early on!
He fights against Team Plasma with everyone else and no villains acknowledge him or give him any special attention, so if you dislike the theory (because you hate the idea of Cilan hiding such a dark secret, wrote it off when the games denied it, because the Shadow Triad never make an appearance in the anime, or any other reason!), there's no solid evidence Cilan is anything more than he seems to be, so take heart!! ♥