Our personality is what makes us unique as humans, so it only makes sense that when we try to mimic human-human interaction, we try to attach a unique personality to a bot. After overcoming some of the technical barriers of building bots, creating their personalities is probably one of the biggest challenges, and we are going to see very interesting developments in this space.
Building a bot's personality is a multifaceted process that includes many factors and parameters, such as the look and feel of the bot, language, style, tone, and voice. It requires us to start by identifying our clients' personas – their language, their age range, their style, and so on – in order to match them with the best "agent." We can end up with a serious, trusted bot, or a funny, silly one. In each case, the bot has to speak its users' "language."
Where possible, it is even recommended to create multiple personas for a bot, if you know in advance that you are targeting more than one type of person/client...