Ennis William Cosby (April 15, 1969 – January 16, 1997), the only son of American comedian Bill Cosby, was murdered on January 16, 1997, near Interstate 405 in Los Angeles, California. He was shot in the head by 18-year-old Mikhail Markhasev in a failed robbery attempt. Cosby was 27 years old.

Cosby's death resulted in significant media coverage, public outrage and an outpouring of support for the Cosby family. Seeking the $100,000 reward offered by the National Enquirer, an acquaintance of the shooter provided information that led to Markhasev's arrest in March 1997.

Subsequently, Markhasev was tried and convicted of first-degree murder and attempted robbery on July 7, 1998, and was sentenced to life in prison the following month. Markhasev maintained his innocence until 2001, when he admitted to committing the murder and asked that appeals in his case stop.

Ennis William Cosby was born April 15, 1969, to actor and comedian Bill Cosby and his wife, Camille Cosby (née Hanks). He was their third child and only son. Cosby had four sisters: Erika (b. 1965), Erinn (b. 1966), Ensa (April 8, 1973 – February 23, 2018), and Evin (b. 1976). When Camille was about to give birth to Ennis, Bill joked during a television special: "It had better be a boy, you hear, Camille?" and Camille responded: "Right!" from offscreen.

Cosby was born at Cedars-Sinai Medical Center Los Angeles and grew up in Southern California, Pennsylvania, and New York City. He attended George School, a private boarding school outside Philadelphia, where he played football, basketball, lacrosse, and track and field. He suffered from undiagnosed dyslexia, which caused low grades and friction with his parents, both of whom had advanced educational degrees.

Ennis' childhood is a focus of his father's 1982–83 stand-up release Himself, and he is also referred to in a routine from Eddie Murphy's 1987 concert film Raw. Theo Huxtable, Bill Cosby's television son on The Cosby Show, was based on Ennis, and this was reflected in storylines with Theo struggling in school until he was diagnosed with dyslexia. It was also written into the script that Bill's character, Cliff Huxtable, had been wrong in blaming Theo for his poor grades; this mirrored Bill Cosby's real life, as he had felt guilty for thinking Ennis had struggled academically because of a character flaw.

Cosby's dyslexia was diagnosed when he entered Morehouse College in Atlanta, where a friend encouraged him to be tested. He then spent a summer semester in Putney, Vermont, undergoing intensive academic training at Landmark College, a private university established exclusively for students with learning disabilities. Cosby later returned to Morehouse, where he made the dean's list when his grade point average jumped from 2.3 to more than 3.5.

In his free time, Cosby tutored students at elementary and high schools and earned a Morehouse bachelor's degree in 1992, which he followed with a master's from Columbia University in New York in 1995. While at Columbia, he worked at Alfred E. Smith Elementary School and also tutored students struggling with learning disabilities. His friends recalled that he kept a low profile and did not want special treatment, and would just say that his father worked "in business" when asked why he had lived in three states.