1. A system comprising a user device and one or more storage devices on which are stored instructions that are operable, when executed by the user device, to cause the user device to perform operations comprising: receiving, by a computer-implemented agent specific to the user device, a digital representation of speech encoding an utterance; in response to processing the digital representation of the speech to determine the words included in the utterance, determining, using the utterance, to request input identifying a sentiment of a user who spoke the utterance; in response to determining to request the input identifying a sentiment of the user who spoke the utterance, presenting a request for user input identifying a sentiment; in response to presenting the request, receiving user input identifying a sentiment of a speaker of the utterance; determining, by the computer-implemented agent, that the utterance specifies a request for another computer-implemented agent that is a different computer-implemented agent than the computer-implemented agent by: determining, by the computer-implemented agent using the utterance, that the utterance is not specific to a particular second computer-implemented agent; in response to determining that the utterance is not specific to a particular second computer-implemented agent, determining, by the computer-implemented agent using the utterance, two or more second computer-implemented agents each of which can respond to the utterance; in response to determining the two or more second computer-implemented agents each of which can respond to the utterance, automatically selecting, without receiving user input, one of the second computer-implemented agents each of which can respond to the utterance; and in response to automatically selecting, without receiving user input, one of the second computer-implemented agents each of which can respond to the utterance, determining, by the computer-implemented agent, that the utterance specifies a request for the selected one of the second computer-implemented agents; providing, by the computer-implemented agent to the other computer-implemented agent, a representation of the utterance and data identifying the sentiment and user profile data for a user who spoke the utterance to enable the other computer-implemented agent to automatically complete a transaction using the user profile data without requesting, from the user, data that is included in the user profile data; receiving, by the user device, a response to the utterance for the other computer-implemented agent that was determined using the sentiment; and in response to receiving identification of the response, presenting, by the user device, the response to the utterance received from the other computer-implemented agent that was determined using the sentiment.