Lucius Malfoy slipped Ginny Weasley the diary in Diagon Alley, and we know the reason he did so was to a) harm as many Mudbloods as possible, and b) to harm the Weasley family and their reputation.
He planted the powerful Dark object on Ginny Weasley, hoping that her involvement in the murder of Muggle-born children at Hogwarts would reflect poorly on Arthur Weasley and that he would lose his job. This would leave the despicable Lucius Malfoy free to own all the Dark objects he desired without pesky Mr.
Unbenownst to her the diary was in fact cursed, and by writing in it she was feeding the spirit of a young Lord Voldemort who had used the diary as his first Horcrux. As she succumbed to the dark magic Ginny was forced to re-open the Chamber of Secrets and release one of Hogwarts' darkest secrets.
Lucius Malfoy didn't seem to understand just how valuable the diary actually was to Voldemort or that it contained a piece of his soul. He just thought it was an excellent way to get rid of Muggle-borns.
Lucius planted the diary on Ginny in a plot to use her to reopen the Chamber of Secrets, which would lead to attacks on Muggle-born students. Lucius knew the diary is cleverly enchanted, but was not aware that it contained a part of Voldemort's soul.
The REAL Reason Lucius Gave Ginny Tom Riddle's Diary
Why was the diary given to Ginny?
In secret, Malfoy kept the diary before he slipped it, unnoticed, into Ginny Weasley's cauldron of school supplies at Flourish and Blotts in 1992. The diary used its dark magical influence to bewitch and force Ginny to re-open the Chamber of Secrets, but it was destroyed by Harry Potter in 1993 with a Basilisk's fang.
When Lucius turns on Voldemort due to the reveal of his Horcruxes, Narcissa divorces him, taking 75% of Malfoy's wealth with her. Even her relationship with Draco is different, with POS-Narcissa only viewing Draco as a tool to further her own agenda.
Initially a devoted follower of Voldemort, Lucius eventually abandons his loyalty to protect his family. This change becomes evident during the Battle of Hogwarts, where he prioritizes the safety of his son over his allegiance to the Death Eaters.
Lucius and Narcissa were loving parents who spoiled their son. They never abused him verbally or physically, they never neglected his needs and never left him wanting. However they were more or less dangerous people, in their associations and beliefs. They taught Draco prejudice.
Lucius Malfoy did nothing to dispel this hateful impression and was a fully signed up supporter of pure-blood supremacy. In fact, he was in Lord Voldemort's closest circle as a Death Eater. He despised Muggles, Muggle-borns, those he saw as blood traitors and tried to instil those values in his family.
Harry Potter, Ron Weasley, and Gilderoy Lockhart came to the rescue. Ron and Lockhart were stuck behind an avalanche of stone, so the battle was fought mostly by Harry. Harry managed to defeat both the Basilisk and the memory of Tom Riddle, thus saving Ginny's life.
She remains unattached and taken with Harry until she hooks up with Michael Corner, a Ravenclaw student. That relationship ends in Harry Potter and the Order of the Phoenix, after Ginny breaks up with him and Michael shifts his attention to Cho Chang.
Later, Ginny, having seen the diary amongst Harry's books, stole the diary from among Harry's room, fearing that Riddle would tell Harry about her feelings towards him, and shortly thereafter went missing.
Dumbledore was also aware that Voldemort had split his soul into multiple pieces for Horcrux creation after his study of the diary and the collected memories of Tom and the altered memory of Slughorn.
It is true that towards the end of the second book and movie, Harry Potter and the Chamber of Secrets, Dumbledore insinuates that he knows Lucius planted the diary on Ginny, but he never says it.
In 1992, Lucius Malfoy came to Borgin and Burkes to sell him several dark objects and poisons, fearing that the Ministry of Magic would soon be investigating his mansion.
Harry Potter had a few love interests during his time at Hogwarts. Though he eventually settled down with Ginny Weasley, he also had a thing for Cho Chang in his earlier school years. Then, of course, there's his secret love for Draco Malfoy…
He fell in love with Astoria Malfoy, who didn't meet his family's pure-blood expectations, and was even willing to let the Malfoy bloodline end to protect her. This shift in Draco's beliefs shows his growth and development as a character throughout the series.
Lucius Malfoy was one of the many Death Eaters who denied their allegiance to Voldemort after the end of the First Wizarding War and therefore would be a perfect example of the kind of person Barty Crouch Jr. hates the most.
Lucius Malfoy appeared weak because he was under the constant strain under Lord Voldemort. His son had already failed him in not having enough courage to kill Dumbledore and also, his family's life and his were under constant threat of death as they didn't search for Lord Voldemort when he was not fully functional.
When asked what shape Draco's Patronus Charm is, Rowling replied that, at least by the end of the sixth book, Draco was not capable of producing a Patronus, as it is not magic routinely taught at Hogwarts.
During this year, Narcissa became pregnant and miscarried. She was distraught and uncertain of what to tell Lucius, as she had not told him of her pregnancy. Shortly thereafter, he brought her out to the Leaky Cauldron to visit with his friends Vettlingar Yaxley and Thorfinn Rowle.
Narcissa and Lucius both enjoyed being members of the social elite, and loved and spoiled their only child. Unlike Bellatrix, who did not hold love for her husband, Narcissa truly loved Lucius. Narcissa was very upset when he was briefly imprisoned in Azkaban and became defensive when others mentioned his failures.
Narcissa, the youngest of all three, made a respectable marriage after graduating Hogwarts, and into another pure-blood family. It was Lucius Malfoy, a Death Eater, who brought Narcissa into the darker side of the wizarding world – but tellingly, Narcissa never became a Death Eater herself.
