Randy is characterized as a naïve, loyal, overly ambitious but not necessarily bright assistant to Stottlemeyer. His far-fetched theories and comments about the cases Monk works on are a running gag of the series. Apart from his extremely ridiculous theories, which often involve defying the very laws of physics, Disher appears rather competent within his own range of abilities. He has proven himself to be trustworthy, courageous, and capable of providing valuable insights into the cases they tackle. Also, a running gag is the awkwardly ceremonial way in which he delivers news to Stottlemeyer, asking him to guess what it is or sit down for it. His personality has dramatically changed throughout the years. Originally, he was not only skeptical of Monk, but he seemed to find Monk a joke. One could assume that he was jealous of Monk, by his actions toward Monk himself and to the captain about him. However, he was still bumbling, as he gave Monk his gun during a frantic scene in "Mr. Monk and the Candidate". He was also known to drink on the job when he becomes intensely stressed, as evidenced in "Mr. Monk Gets Married" when Randy Disher grew stressed in regards to his mother marrying a significantly younger antique dealer, marrying him after the second date, and then claiming they have marital problems necessitating a visit to a marriage counseling house shortly after their marriage, all while his mother was neither beautiful nor does she even have a lot of money, thus drinking some alcohol while hiring Monk and Sharona to take the case in regards to finding out what the antique dealer is up to while inebriated.
It is revealed in one of the Monk books "Mr. Monk and the Blu Flu" it is shown that Disher has the best conviction and closure rate. Mainly because Capt. Stottlemeyer gives him normal and not high profile cases. Also, strangely he is often used to be a female impersonator, such as in "Mr. Monk and the Kid" and "Mr. Monk and the Three Julies," though Sharona saw through the former instance.
- In the pilot episode, Randy was credited as "Lieutenant Randy Deacon".
- Randy is allergic to cats as well as peanut butter.
- Randy is left-handed.
- Randy is usually seen driving a 2003 tan Ford Crown Victoria with a Mars light attached to the inside rearview mirror, but mentions in Mr. Monk Can't See a Thing that he also drives a Ford Festiva.
- Although Randy claims that he has no uncles, only aunts, in Mr. Monk Gets Cabin Fever, he inherits a farm from his uncle, Harvey Disher, in Mr. Monk Visits a Farm.