Irish is a member of the Black Organization who appears as the main antagonist in the story. Physically, he is a large, imposing man and is left-handed. Very little is known about his past, but his most significant personal connection is to a fellow operative named Pisco, whom he greatly admired and considered a father figure. This admiration turned into a deep and bitter grudge when Gin cold-heartedly executed Pisco and left his body to burn, an event that profoundly shapes Irish's actions.

Irish is a highly capable and intelligent operative, yet he occupies a complex position within the Organization. While he is not a top leader, his rank is significant enough that he can contact the boss directly. However, other members like Gin treat him as a subordinate and scold him, showing that his standing is not unassailable. His primary motivation in the story is driven by his loyalty to Pisco and his hatred for Gin. He seeks revenge not through direct confrontation, but by attempting to disgrace Gin before the Organization's leadership. To do this, he plans to present evidence of a critical mistake Gin made: failing to kill the young detective Shinichi Kudo, whose survival would prove Gin's incompetence.

To execute this plan, Irish infiltrates the Tokyo Metropolitan Police by disguising himself as a high-ranking officer. He is highly skilled in disguise, a talent that allows him to move freely and monitor a major investigation, although his large stature limits him to impersonating individuals of a similar build. His true goal is to retrieve a data card that contains a list of the Organization's undercover agents. While following the police investigation, he grows curious about Conan Edogawa, the child frequently assisting the police. Through careful observation and research, including fingerprint analysis, Irish deduces that Conan is, in fact, Shinichi Kudo, the very target he intends to use against Gin.

Irish possesses a range of formidable abilities. He is a skilled martial artist whose powerful physique allows him to easily defeat multiple opponents, including a group of police officers. He is one of the few individuals capable of holding his own in a hand-to-hand fight against the karate champion Ran Mouri, though his victory is partly due to surprise. He is also extremely proficient with firearms, demonstrating pinpoint accuracy by destroying Conan's high-tech gadgets without harming the boy himself. Like many Organization members, he has a very high tolerance for pain, remaining conscious and functional even after suffering a severe fall and being shot.

His personality is ruthless and he shows no hesitation in using lethal force against anyone who gets in his way. He also seems to take a certain enjoyment in challenges and confrontations, appreciating Ran's fighting skill and even toying with Conan as he hunts him through Tokyo Tower. Despite this cruelty, he develops a degree of respect for Conan's abilities and tenacity. His key relationships are defined by his mission: he holds a deep enmity toward Gin, who regards him with cold disdain, and he is acquainted with Vermouth, who appears to show him a modicum of respect.

In the final confrontation, after Irish has recovered the data card and cornered Conan, the Organization arrives in a helicopter. Gin, having learned that Irish's cover is blown, coldly orders his execution. Irish is shot by the sniper Chianti but is not killed instantly. As Conan tries to drag him to safety, Gin orders a second shot. In his final act, Irish uses his own body to shield Conan from the bullet, a choice that is a dramatic shift from his earlier ruthlessness. His dying words to Shinichi Kudo are a challenge to keep pursuing the Black Organization, signifying that he has ultimately placed his faith in his young enemy to carry on the fight.