Mark Cassius Ferguson (born November 30th, 1963), simply known as Mark Cassius, is a Canadian singer, songwriter, dancer, actor, and musician. He is best known for his work as a member of world-renowned a cappella group The Nylons from 1997 to 2005,  and for his work in musical theatre.
Cassius was born in Chaguanas, Trinidad and Tobago, and attended high school at St. Mary's College CIC in Port of Spain. His parents separated while he was very young; his father, a policeman, moved to Mississauga, Ontario, while his mother, a school principal, remarried. Cassius was raised mostly by his stepfather, now deceased.
Cassius completed a grade 13 year at a high school in Mississauga. During this year, he visited Sheridan College as part of a field trip, and as a result of the visit, he decided to attend Sheridan, graduating from their Music Theatre Performance program in 1985.  In his Alumni Profile for Sheridan College, Cassius states "I was aiming for university but a series of events steered me to college. Thank goodness, because I would not have learned to dance had I enrolled in an opera program. And dance has been a huge part of my success." 
Cassius has starred in numerous musicals, both on and off Broadway. Notable works he has appeared in include Cats, Shenandoah, Joseph and the Amazing Technicolor Dreamcoat (as a member of the original 1992-1993 Canadian company, alongside Donny Osmond), Miss Saigon, Showboat, Ragtime, and Jesus Christ Superstar.   He has performed in such events as the Shaw Festival in Niagara-On-The-Lake and the Stratford Festival,  and has travelled the world as a part of his career.
In 1997, after his part in the Toronto run of Ragtime, Cassius became a member of a cappella group The Nylons, replacing Gavin Hope. As a member, he sang baritone and wrote original pieces for the group.  He recorded two CDs with them: "A Wish for You" and "Play On".  Cassius ultimately left The Nylons in 2005, to be replaced by Tyrone Gabriel; on May 30th, 2014, along with other former members of the band, he performed with The Nylons for a reunion concert at the Young Centre for the Performing Arts in Toronto, as part of the SING! Festival.