T'Kar was a male Klingon alive during the mid to late-24th century. In his adult life, he served as a mercenary and, along with Yeto, was one of two Klingons employed by the Trill Verad to steal the Dax symbiont in the 2370s.
In early-2370, T'Kar was hired by Verad to provide muscle during his failed attempt to forcibly join with the Dax symbiont. T'Kar was annoyed by the Federation and opposed to their alliance with the Klingon Empire, stating that the Empire was ruled by "doddering fools and frightened old women."
After securing Deep Space 9, T'Kar guarded the hostages they had taken and kicked Operations Chief Miles O'Brien in his arm when he attempted to discuss the situation with Commander Benjamin Sisko, causing O'Brien severe pain due to a phaser blast he had sustained earlier.
"This is a nice way to showing your gratitude. We just saved your lives out there."
"You see? The ever-helpful Federation. So predictable."
- - Miles O'Brien and T'Kar
"The Empire is governed by doddering fools and frightened old women who aren't worthy of the name Klingon."
- - T'Kar
"Your turn, little man."
- - T'Kar, to Julian Bashir
- - Quark and T'Kar, following a fight between the two
T'Kar was played by actor Tim Russ, who later went on to play Lieutenant Tuvok in Star Trek: Voyager as well as his mirror universe counterpart in DS9: "Through the Looking Glass". Russ previously appeared in the Star Trek: The Next Generation episode "Starship Mine", in which he also played the role of a mercenary. Coincidentally, the starship on which his character arrived in that episode used the same studio model as featured in "Invasive Procedures".
The script for "Invasive Procedures" describes T'Kar as, "a grizzled Klingon mercenary". 
The mirror universe version of T'Kar appears in the novella "The Mirror-Scaled Serpent", in which he is a member of the Obsidian Order belonging to the Klingon-Cardassian Alliance. The story also reveals that, prior to joining the Terran Rebellion in the 2370s, Tuvok was his slave for many years. This was an in-joke based on the fact that both characters were played by Tim Russ.