| Thomas Gregson |
|Affiliation||New York City Police Department|
|Family||Cheryl Gregson (wife)|
|Behind the scenes|
|Portrayed by||Aidan Quinn|
Captain Thomas "Tommy" Gregson is the captain of the 11th precinct in the New York City Police Department, and a primary character in Elementary. He works alongside Detective Marcus Bell. He is Sherlock Holmes' police contact and supervisor.
In "Pilot", he states that after the 9/11 attacks he was sent over to London to observe how the New Scotland Yard operate counter terrorism which is where he met Sherlock who was, at the time, working homicide.
In "The Rat Race", Joan, who has been out of contact with Sherlock for too long, is afraid he relapsed and has no choice but to reveal herself as a sober companion for Sherlock to Gregson. Gregson later reveals to Sherlock that he had known about his problem for some time. He agrees to keep a lid on this information from everyone else.
In "One Way to Get Off", Holmes helped Gregson investigate a new killer who repeated the methods of serial killer Wade Crewes, who had been arrested for the previous crimes in 1999. Although the subsequent investigation revealed that Gregson's ex-partner had planted the evidence that convicted Crewes, Sherlock was also able to discover that the new murders were being commited by Crewes' son, Sean Figueroa, to try and clear his father, allowing Sherlock and Gregson to halt the new crimes and confirm Crewes' guilt.
In "Dead Man's Switch", after witnessing the murder of blackmailer Charles Milverton, Sherlock went to ask Gregson for help in deciding what to do given the complexities of the current case, citing Gregson as an investigator he both respected and admired; if Milverton's death was exposed, his accomplice was under orders to release Milverton's blackmail material on all his 'clients'. Their subsequent investigation discovered that Milverton had been killed by his new partner after eliminating the old one.
- Gregson's name was initially given, in press information prior to the show airing, as "Captain Tobias "Toby" Gregson". However, his name was later confirmed to be "Captain Thomas "Tommy" Gregson".
- He has daughters, though it is not specified how many. ("Dead Man's Switch")
- He and his wife are not living together though they are not divorced. ("An Unnatural Arrangement")