Dr. Mary Alice Anders worked for the US Atomic Research Center where she met Otto Octavius. Eventually, she and Otto became engaged. Otto's mother thought of this as her son abandoning her and was horrified. Otto broke off the engagement.
Rumor has it that he had his cousin who also worked with the lab have her dismissed from her position.
At one time the Green Goblin gave her a virus in order to make Doc Ock do his biding.
Later in life, Otto found that his mother was seeing a man and snapped on his mother for being a hypocrite. The argument caused his mother to have a heart attack from which she died.
Although they may not have spoken, Otto still cared for her deeply. He eventually stole some blood samples and radioactive isotopes to try and cure her disease. He failed and she died of AIDS.