Idoia López Riaño was born on March 18, 1964, in San Sebastián, in the Basque Country of northern Spain. Raised in what was described as a stable family with a relatively normal upbringing, she received a decent education and was not known for early involvement in crime or political extremism. However, as the Basque independence movement grew more radical in the late 1970s and early 1980s, her trajectory changed dramatically.

At the age of 16, Riaño was recruited into Euskadi Ta Askatasuna (ETA), the Basque separatist group that waged a violent campaign against the Spanish state in pursuit of independence. She was drawn into the organization through her boyfriend, José Ángel Aguirre Aguirre, a member of ETA. At the time, ETA was transitioning from a nationalist movement into one of Europe’s most lethal separatist terrorist groups.

Riaño’s involvement deepened as she gained a reputation within the group for her intelligence, charisma, and striking appearance — qualities she reportedly used as part of her operational tactics. Nicknamed "La Tigresa" (The Tigress), she was notorious for using seduction to obtain information, particularly targeting police officers and military personnel. This manipulation allowed ETA to plan assassinations and bombings with precision.

By her early twenties, Riaño had risen to become a lieutenant in ETA’s Madrid cell. Her loyalty to the cause and willingness to kill for it made her one of the organization’s most dangerous operatives.

At only 20, Riaño committed her first known political murder on November 16, 1984, when she, her boyfriend, and a third conspirator executed Joseph Couchot, accused by ETA of being a GAL member. Over the next two years, she participated in several high-profile attacks:
February 26, 1985 — Murdered Ángel Manuel Facal Soto
May 12, 1985 — Killed Police officer Máximo García Kleiner
June 17, 1986 — Involved in a triple assassination of military figures using a submachine gun
July 14, 1986 — Orchestrated a car bomb attack in Plaza República Dominicana, Madrid, killing 12 Guardia Civil. 

In total, she was charged with 23 murders between 1984 and 1986. Her tactics combined ruthless efficiency with calculated manipulation—attacks designed to shock political structures and sow terror.

On August 28, 1994, French authorities arrested Riaño in Aix-en-Provence alongside her partner. She served five years in France before being extradited to Spain on May 9, 2001. In 2002, she was convicted and sentenced to over 2,000 years in prison for her role in the ETA killings. During the trial, she defiantly declared her steadfast commitment to ETA's cause.

While imprisoned, she married twice (2004 and 2006), renounced violence through the “Vía Nanclares” approach, and publicly apologized—actions that led to her expulsion from ETA and eventual early release. Her conduct in prison and rehabilitation efforts contributed to parole. On June 13, 2017, after serving 23 years (one per victim), she was released. Her release generated significant media attention in Spain.