BANGALORE, India — On the evening of Sept. 5, I got a call from my wife, a fellow journalist. “Gauri Lankesh has been shot outside her house,” she said. “She is dead.” Ms. Lankesh, 55, was the editor of Gauri Lankesh Patrike, a weekly newspaper, which she published from Bangalore, India, in the southern state of Karnataka.

I drove with two journalist friends to the morgue of a hospital where her body was. At 8 p.m., she had been entering her home in the upper-class area of Bangalore when an assassin on a motorbike fired at her and fled. Three bullets hit her, damaging her heart and lungs, according to the post-mortem report.

I had known her for 10 years. All I ever did was argue with her. Our arguments had acquired an increasing intensity in the three years since Narendra Modi came to power and India turned toward majoritarianism and intolerance. An outspoken critic of Prime Minister Modi’s Hindu nationalist government, she said in her last editorial that spreading fake news had contributed to the success of Mr. Modi and his party.

After Rohith Vemula, a Dalit graduate student and activist at a university in the southern city of Hyderabad, killed himself in January 2016 because of intense, unceasing institutionalized caste discrimination, a coalition of Dalit (lowest caste) and leftist student groups sought the prosecution of university officials and the right-wing Bharatiya Janata Party politicians, who had pushed him to the brink. The leftist groups dominated by upper-caste Hindus were not willing to work under the leadership of Dalit activists.

I was agitatedly talking to Ms. Lankesh about how the Indian left was almost entirely led by upper-caste Hindus. Ten years of reporting on caste prejudice and politics and my personal history of growing up and working as a Dalit writer made me believe that even in struggles for civil and political rights, the Indian left excluded the Dalits from positions of leadership. Ms. Lankesh didn’t see leadership as a big question when in the context of the more pressing need to fight the rise of Hindu nationalism, which she described as “fascism.”

She mockingly asked me, “And where are the Dalit women leaders?”

I replied sarcastically, mentioning something about privilege.

She was enraged. “Yes, I am rich, I live in a big house and I am very privileged,” she said. “Come up with a better argument for why, as a woman, I should not be part of the anti-caste struggle. Go read Ambedkar properly!”

The conversation ended and I thought we would never speak again.

I met her a little later at a lecture in Bangalore. She held my hand for a long while after the talk and introduced me to everyone as her son. A few days later, she messaged me with kind words about an article I had written. And she wanted to watch “Madras,” a movie by Pa Ranjith, a young Dalit filmmaker.

Ms. Lankesh was also an effective political organizer with the ability to bring together social and political groups — Dalits, indigenous tribals, leftists, Muslims and others — opposed to the Hindu nationalist attempts to transform India into a country primarily for the Hindus.

The priests at a temple in Udupi, a southern Indian town — a stronghold of the Hindu nationalist movement — were segregating the lower castes, especially Dalit devotees, from the upper-caste Hindus. Last September, Ms. Lankesh helped persuade numerous progressive, Dalit and leftist groups, and nongovernmental organizations — who loathe working together because of political differences — to come together in a march to protest segregation at the Udupi temple. The question of whether Dalits will get to lead the struggle for their rights returned. Ms. Lankesh negotiated with every group to ensure that the upper-caste leaders didn’t appropriate the march.

A month earlier, in July 2016, hard-line Hindu activists had stripped and flogged four Dalit men in Gujarat, the home state of Mr. Modi, for skinning a cow. Thousands of Dalits earn their meager livelihood from skinning dead cows and buffaloes and selling their hides to leather traders. Jignesh Mevani, a young Dalit lawyer, organized and led huge protests in Gujarat against the cow vigilantes.

Ms. Lankesh settled the question of leadership by getting everybody to agree that Mr. Mevani should lead the march against segregation to Udupi temple. Around 10,000 people joined the march. The opposition unity made an impression.

Soon after that I saw my social media timelines filled with photographs of Ms. Lankesh hugging Mr. Mevani and Kanhaiya Kumar, Umar Khalid and Shehla Rashid, leftist student leaders from a university in New Delhi. She called them “her children.” It was her way of creating unity among various groups opposed to the rise of the majoritarian politics.

On the night of her murder, I stood outside her house with our common friends and we wondered why anyone would kill her. She wasn’t the only outspoken critic of the Hindu right. Her newspaper, which was critical of Mr. Modi’s government and the Hindu nationalists, didn’t sell more than a few thousand copies although it was much respected.

I wondered if they killed her because she was a member of the Lingayatcommunity in Karnataka, which wants to separate from Brahmanical Hinduism. In the past few months, the Lingayat leaders had mobilized hundreds of thousands of supporters in public rallies. The mobilization threatens the chances of the Hindu nationalist B.J.P. in the forthcoming state elections in Karnataka. Although Ms. Lankesh supported the call, the Lingayat movement had other, enormously powerful leaders.

In August 2013, the activist Narendra Dabholkar, who campaigned against religious superstitions, was murdered. In August 2015, M. M. Kalburgi, a scholar and outspoken critic of idol worship among Hindus, was gunned down at his own doorstep. In February 2015, Govind Pansare, a Communist leader, community organizer and columnist, was killed in a small town near Mumbai.

Mr. Dhabolkar, Mr. Kalburgi and Mr. Pansare were murdered by assassins on motorbikes, who hid their faces with helmets and fled after the murder. Exactly as Ms. Lankesh was killed.

The murdered intellectuals also wrote in regional languages and worked as activists. Each of them shared the quality of being acceptable to the leftist groups and Dalit groups. They could bring together communities opposed to the Hindu right.

We don’t know yet who killed Ms. Lankesh, but various supporters of Mr. Modi, the B.J.P. and its parent organization, the Hindu nationalist mother ship, Rashtriya Swayamsevak Sangh, celebrated her murder on social media.