Tolaris was a Vulcan and a crew member aboard the Vahklas, a civilian transport ship encountered by Enterprise in 2151. Tolaris and the rest of the crew were considered V'tosh ka'tur ("Vulcans without logic") by other Vulcans for exploring a balance between logic and emotions. Tolaris forged a bond with T'Pol, and suggested she attempt to re-connect with her emotions. He used an ancient Vulcan technique known as a "mind meld" to help her achieve this, but T'Pol was uncomfortable with it and asked him to stop. Tolaris became angry, refused to stop the meld, and assaulted T'Pol through his actions. T'Pol was then forced to violently tear herself away, leaving both parties with mental trauma.
When Enterprise captain Jonathan Archer confronted Tolaris the next day, he brushed it off, eventually losing control of his emotions and tossing Archer across the room. Archer, armed with a phase-pistol, then asked the Vulcans to leave his starship.
From her forced meld with Tolaris, T'Pol contracted Pa'nar Syndrome, a disease that was precipitated by mind-melding improperly. She was later cured of the disease by a meld with T'Pau, a more experienced melder, in 2154. (ENT: "Stigma", "Kir'Shara")