Taleb Jawad al-Abdulmohsen had been living in Germany since 2006 and practised as a psychiatrist in the town of Bernburg, near Magdeburg. He had no known links to jihadists.
Abdulmohsen was arrested in the car used for the attack, and is suspected of deliberately ploughing into the crowd of Christmas revellers in northern Germany on Friday night, killing five and injuring more than 200.
The ramming came eight years to the day after a similar attack on a Christmas market in Berlin that killed 13 people.
The authorities in Germany said the date was not a coincidence, although they have not said it was an Islamist attack.
On social media, Abdulmohsen portrayed himself as a victim of persecution who had renounced Islam and decried what he said was the Islamisation of Germany.
He came from a Shiite family in the village of Hofuf in the predominantly Shiite province of al-Ahsa, in the east of Saudi Arabia.
He arrived in Germany in 2006 and was granted refugee status 10 years later, according to German media and a Saudi activist.
Abdulmohsen lived and worked in the region of Saxony-Anhalt, whose capital Magdeburg is 130 kilometres (80 miles) west of Berlin.
In an interview with the German newspaper Frankfurter Rundschau several years ago, he said he had been threatened with death for apostasy.
In an unpublished interview with AFP from 2022 for an unrelated story, Abdulmohsen presented himself as "a Saudi atheist", and said that young Saudis were not only fleeing the government but "are fleeing Islam".
"Strict Islamic upbringing is the cause of all the problems of Muslims, especially women," he said.
Some media outlets have reported links between Abdulmohsen and the far-right in Germany. He was well-known in the Saudi diaspora in the country and helped asylum seekers, particularly women.
"He is a psychologically disturbed person with an exaggerated sense of self-importance," Taha Al-Hajji, legal director of the Berlin-based European Saudi Organisation for Human Rights, told AFP.
"This is definitely not an Islamist-motivated attack," he added.
Hajji said Abdulmohsen was "a pariah" among the Saudi community in Germany, despite his work with asylum seekers.
Last August, he posted on social media: "Is there a path to justice in Germany without blowing up a German embassy or randomly slaughtering German citizens? I have been seeking a peaceful path since January 2019 and have not found it. If anyone knows it, please let me know."
In the post, he condemned what he called "the crimes committed by Germany against Saudi refugees and the obstruction of justice, no matter how much evidence was presented to them".
