RMS Olympic was a British ocean liner and the lead ship of the White Star Line's trio of Olympic-class liners. Olympic had a career spanning 24 years from 1911 to 1935, in contrast to her short-lived sister ships, RMS Titanic and the Royal Navy hospital ship HMHS Britannic. This included service as a troopship with the name HMT Olympic during the First World War, which gained her the nickname "Old Reliable", and during which she rammed and sank the U-boat U-103. She returned to civilian service after the war and served successfully as an ocean liner throughout the 1920s and into the first half of the 1930s, although increased competition, and the slump in trade during the Great Depression after 1930, made her operation increasingly unprofitable. Olympic was withdrawn from service on 12 April 1935, and later sold for scrap, which was completed by 1939.

Olympic was the largest ocean liner in the world for two periods during 1910–13, interrupted only by the brief service life (six-day maiden voyage in April 1912) of the slightly larger Titanic, which had the same dimensions but higher gross register tonnage, before the German SS Imperator went into service in June 1913. Olympic also held the title of the largest British-built liner until RMS Queen Mary was launched in 1934, interrupted only by the short career of Titanic; Britannic, intended as a liner, instead served as a Royal Navy hospital ship for her 11-month life (December 1915 to November 1916), sinking when she hit a mine.

Built in Queen's Island, Belfast, Ireland, Olympic was the first of the three Olympic-class ocean liners – the others being Titanic and Britannic. They were the largest vessels built for the British shipping company White Star Line, which was a fleet of 29 steamers and tenders in 1912. The three ships had their genesis in a discussion in mid-1907 between the White Star Line's chairman, J. Bruce Ismay, and the American financier J. Pierpont Morgan, who controlled the White Star Line's parent corporation, the International Mercantile Marine Co. The White Star Line faced a growing challenge from its main rivals Cunard, which had just launched Lusitania and Mauretania – the fastest passenger ships then in service – and the German lines Hamburg America and Norddeutscher Lloyd. Ismay preferred to compete on size and economics rather than speed and proposed to commission a new class of liners that would be bigger than anything that had gone before as well as being the last word in comfort and luxury. The company sought an upgrade in their fleet primarily in response to the largest Cunarders but also to replace their largest and now outclassed ships from 1890, RMS Teutonic and RMS Majestic. The former was replaced by Olympic while Majestic was replaced by Titanic. Majestic would be brought back into her old spot on White Star's New York service after Titanic's loss.

The ships were built in Belfast by Harland & Wolff, who had a long-established relationship with the White Star Line dating back to 1867. Harland and Wolff were given a great deal of latitude in designing ships for the White Star Line; the usual approach was for the latter to sketch out a general concept which the former would take away and turn into a ship design. Cost considerations were relatively low on the agenda and Harland and Wolff was authorised to spend what it needed on the ships, plus a five per cent profit margin. In the case of the Olympic-class ships, a cost of £3 million for the first two ships was agreed plus "extras to contract" and the usual five per cent fee.

Harland and Wolff put their designers to work designing the Olympic-class vessels. It was overseen by Lord Pirrie, a director of both Harland and Wolff and the White Star Line; naval architect Thomas Andrews, the managing director of Harland and Wolff's design department; Edward Wilding, Andrews' deputy and responsible for calculating the ship's design, stability and trim; and Alexander Carlisle, the shipyard's chief draughtsman and general manager. Carlisle's responsibilities included the decorations, equipment and all general arrangements, including the implementation of an efficient lifeboat davit design.

On 29 July 1908, Harland and Wolff presented the drawings to Bruce Ismay and other White Star Line executives. Ismay approved the design and signed three "letters of agreement" two days later authorising the start of construction. At this point the lead ship – which was later to become Olympic – had no name, but was referred to simply as "Number 400", as it was Harland and Wolff's four hundredth hull. Titanic was based on a revised version of the same design and was given the number 401. Bruce Ismay's father Thomas Henry Ismay had previously planned to build a ship named Olympic as a sister ship to Oceanic. The senior Ismay died in 1899 and the order for the ship was cancelled.

Construction of Olympic began three months before Titanic to ease pressures on the shipyard. Several years would pass before Britannic would be launched. To accommodate the construction of the class, Harland and Wolff upgraded their facility in Belfast; the most dramatic change was the combining of three slipways into two larger ones, allowing Olympic and Titanic to be constructed side by side. Olympic's keel was laid on 16 December 1908 and she was launched on 20 October 1910, without having been christened beforehand. By tradition, the White Star Line never christened any of their vessels and for the launch the hull was painted in a light grey colour for photographic purposes; a common practice of the day for the first ship in a new class, as it made the lines of the ship clearer in the black-and-white photographs. The launch was filmed both in black and white and in Kinemacolor, with only the black and white footage surviving. The launches of Titanic and Britannic were also filmed, though only Britannic's survived. Her hull was repainted black following the launch.

On 1 April 1911, Olympic was pulled into Thompson Graving Dock as part of its opening ceremony. Here, her hull was cleaned and painted. It was also the place where she received her propellers.