Ricky is the capuchin monkey who is part of Amy's ongoing research into addiction in primates. In The Agreement Disssection, he is living as a guest in her apartment. As Amy says Hey, I'm giving him emphysema. The least I can do is to let him hang out and watch cable.
Ricky is "a bit of an ass" who gets pleasure from blowing smoke into Sheldon's face. He also gets angry when the store is out of menthol. Amy concedes there is a downside, in that Ricky might tear her face off while she sleeps, but she is remarkably blithe about her houseguest.