Hulett C. Merritt mansion, Historical mansion in Orange Grove Avenue, Pasadena, US.

The Hulett C. Merritt mansion, also called Villa Merritt Ollivier, is a 17,000-square-foot residence at 99 Terrace Drive with seven bedrooms and three bathrooms. It was built on four acres between 1905 and 1908. In 1966, two Modernist classroom buildings with honeycomb concrete facades were added, flanking the mansion and connected by a formal Italian sunken garden with a central plaza.

Hulett C. Merritt, chairman of US Steel and an iron ore mining magnate, built the Villa Merritt Ollivier on four acres between 1905 and 1908 at a cost of $1,100,000. After his death, Herbert W. Armstrong bought the house in 1956 from Merritt's four surviving grandchildren because it adjoined Ambassador College. It became Ambassador Hall, Terrace Drive was closed, and the address changed to 100 S. Orange Grove Blvd. Ambassador College closed in 1997.

The mansion stood on South Orange Grove Avenue, known locally as "Millionaires' Row" in the City of Pasadena's 1997 Architectural and Historical Survey. Its name Villa Merritt Ollivier was replaced by Ambassador Hall after Herbert W. Armstrong bought the estate in 1956. In 1966 a formal Italian sunken garden with a central plaza was laid out between the mansion and two new classroom buildings.

The property is situated in a residential neighborhood with good street access and is easily reached on foot. Visitors should be aware that the grounds are privately held and general access may be restricted.

The mansion was later purchased by a religious leader who converted it into an educational institution, giving it a completely different purpose. This transformation shows how grand residences were sometimes repurposed for new institutional roles.