James Douglas Muir Leno (born April 28, 1950 in New Rochelle, New York) is an American comedian best known as the host of the popular NBC television program The Tonight Show. He grew up in Andover, Massachusetts, and received his Bachelor's degree in Speech therapy from Emerson College in 1973. He suffers from a slight form of dyslexia.

Known for his work ethic and his "nice" demeanor, Leno started his career as a stand-up comic performing in nightclubs, bars and any place that would give him even five minutes of stage time. Though he had made the occasional foray onto television in the form of guest appearances on The Tonight Show, then hosted by Johnny Carson, stardom eluded him and he continued to work wherever he was allowed. It has been reported that Leno would sometimes work as many as eight or nine clubs in one evening. He began making more frequent appearances on television when many of his friends and contemporaries became more influential on late night programs. Leno made a record number of appearances on Late Night with David Letterman. His popularity was noted by NBC executives, who decided to make Leno the permanent guest host for The Tonight Show when Joan Rivers left that position.

When Carson retired in 1992 Jay Leno became the new permanent host of The Tonight Show after a long period of debate and negotiation between the network, Leno, and David Letterman (who had been considered by many to be Carson's heir apparent); Letterman soon signed a deal with CBS, sparking an ongoing late-night rivalry between the two talk-show hosts. Although Letterman's Late Show led in the ratings from the start, The Tonight Show took over the lead in 1995 and has, on the whole, had higher ratings ever since.

Although known mainly for his wit, he has also shown his sensitive side on air. When The Tonight Show came back after the September 11 terrorist attacks, he nixed his usual monologue to talk about what had happened. He also spoke about the Space Shuttle Columbia disaster. In addition, following the skating controversy surrounding the ice skating pairs event at the 2002 Winter Olympics, Leno invited the Canadian pairs teams onto his show the following day and waved a Canadian flag and played "O Canada" for them.

In 1998, Jay Leno and his show partner Kevin Eubanks were invited to a wrestling show called WCW Road Wild 1998, from Sturgis, South Dakota, to wrestle against Hulk Hogan and WCW President Eric Bischoff.

On May 12, 2003, he and Katie Couric switched places as a publicity stunt, meaning Leno co-hosted the Today Show with Matt Lauer.

On The Tonight Show's 50th anniversary episode, on September 27, 2004, he announced that he would retire in 2009, when his current contract expires; as many expected, Leno announced that Late Night host Conan O'Brien will replace him.

In the ongoing Michael Jackson child sexual abuse trial, Leno is one of the many defense witnesses. He says that by telephone the accuser had begged him for money; during the call Leno could hear the boy's mother coaching him. Leno felt something was wrong and reported it to the police. The accuser says he left a message on Leno's answering machine, but did not speak with him.

At first Leno was not allowed to continue making jokes about Jackson and the case; however, he could and did still write them, and used a stand-in to tell them. At some stage the judge allowed Leno to make jokes, as long as they are not related to this incident.

In automobile collecting circles Jay Leno is known as an avid collector and restorer of cars and motorcycles. He has a very large antique car collection on which he is constantly working in his spare time, and routinely drives cars from his collection from his home to his studio. He is also a promoter of the mechanical crafts, through his columns in Popular Mechanics and his educational activities. Recently Leno auctioned off a Harley Davidson motorcycle signed by his celebrity guests to help the victims of the 2004 Indian Ocean Earthquake, the bike sold for $US800,100.00.