Visitors spawn with a random set of clothes and a randomized name chosen from a set list. See a list of known randomized names here.
Main article: Guest statistics
Depending on what your park has to offer and what a visitor interacts with, their statistics (stats) will change.
Based on statistics, a visitor's thoughts will change. These can be analyzed to determine what to change to improve your park. Specific thoughts can be seen here.
By opening the settings and selecting "Use R15 guest models, the player can change all guest's model type to R15. This affects only the player who selects it and is applied to all guests in all parks.