Lachlan "Lachie" Fraser is a fictional character from the Australian Channel Seven soap opera Home and Away, played by Richard Grieve. He made his screen debut on 19 March 1997 and last appeared on 27 November 1998. He joined the show after previously appearing in rival soap opera Neighbours. Lachlan is introduced as a new doctor working at Summer Bay's local hospital. Grieve had to research the profession and received help from an on-set medical advisor. Lachlan is characterised as a sweet and gentle person who is brilliant at medicine.

During his tenure he strikes up relationships with Shannon Reed (Isla Fisher), Terri Garner (Alyson Standen) and Chloe Richards (Kristy Wright). The latter who becomes pregnant after a one-night stand, Lachlan and Chloe fall in love. She gives birth to a daughter, Olivia. But their relationship is marred by his interfering mother Diana (Kerry McGuire), whom he is unable to stand up to. Grieve decided to leave the show in 1998, which gave producers a dilemma. They had developed the partnership between Lachlan and Chloe in advance. They cast Michael Piccirilli as Lachlan's brother James to take over the relationship with Chloe. Lachlan's exit storyline involved him battling a brain tumour, suffering brain damage after having a cerebral haemorrhage and leaving for treatment in the United States. The character was later killed off-screen.

Grieve was nominated for a Logie Award for portrayal of Lachlan. Reporters from the magazines Inside Soap and Soap Stars have praised the character's sex appeal, while another columnist said he was the show's hero who solved all medical emergencies in Summer Bay.

In January 1997, it was announced that Richard Grieve had taken on the role of Lachlan. He previously appeared in rival soap opera Neighbours. The actor told Jason Herbison from Inside Soap that "I'm thrilled, I'd been looking for a change for a while, so the chance to [...] start work on a different show is great." Grieve relocated from Melbourne to Sydney for the role. Andrea Jones from The Sun-Herald revealed that his character would be introduced as a new doctor working in Summer Bay's local hospital.

I'm going from being a handyman to a doctor, you couldn't really get much further far removed, could you? It's great playing such a different sort of role.

— Grieve comparing his roles as Sam Kratz and Lachlan. (1997)

Lachlan debuted on-screen on 19 March 1997. His initial scenes depict him taking his new position at the hospital where an established doctor, Kelly Watson (Katrina Hobbs), takes a dislike to him because he is considered more experienced, despite them being equally qualified.

Grieve told Helen Childs from Inside Soap that Lachlan is completely different from Sam. He enjoyed playing a doctor because of the "amazing" experiences it created. The actor had to research the profession before taking the part. He also told Childs that "we have a medical advisor on the show who helps with the medical scenes, and she also arranged for me to go to St Vincent's hospital in Sydney to observe some operations." He is characterised as a sweet, gentle, tall, dark and handsome man. A writer from the official Home and Away website said that Lachlan had a "brilliance" about him. His mother, Diana (Kerry McGuire), likes to meddle in her son's lives. Lachaln tolerates her interfering in his business and does not dare to stand up to her.