Are the UCLA Bruins the oldest rival of USC?
No. UCLA and USC have played 79 times with the Trojans leading the series 44-28-7. USC has played more games against Stanford (88), Notre Dame (82), and Cal (98). The two schools first played in 1929, with USC winning the first two games by such lopsided margins (76-0 and 52-0) that the series was suspended for five years. When the series resumed in 1936, the two teams played to a 7-7 tie. The Trojans aren't UCLA's longest played series either; because the teams stopped playing for five years while UCLA was still in the Pacific Coast Conference, California and Stanford have played more games against UCLA.
So what's with the Victory Bell?
When the Los Angeles Normal school became the University of California, Southern Branch it made history as the first multicampus university system in the nation. At 33 years old, Edward A. Dickson became UCLA's champion on the university system's governing board. In 1913 he had been named chairman of the California Railroad Commission. As a progressive Republican, he had worked on reducing the entrenched power of the Southern Pacific Railroad. As a regent and a Southern Californian, he championed the creation of the Southern Campus and it's growth over 43 years. He earned the moniker "Godfather of UCLA", and as best as I can tell this is why in 1939 the UCLA Alumni Association donated a 295 pound bell that used to sit atop a Southern Pacific Railroad locomotive to the UCLA student body.
UCLA students rang the bell after every point, much to the annoyance of USC students. So in 1941 six members of the USC Trojan Knights snuck into the UCLA cheering section and helped load the bell into a truck bound for Westwood. While UCLA students were looking for the key, the Trojan Knights drove of with the bell. The USC students kept the bell hidden, but when it started showing up in USC magazines UCLA students retaliated by painting Tommy Trojans sparking a prank war between the two campuses. The campuses signed the Victory Bell Agreement in 1942 making it a traveling trophy for the annual football game in an effort to thwart any more pranks. USC paid $150 for it's share of the bell, and UCLA won the first Victory Bell game to return the bell to it's original home.
Did that stop the pranks?
No. In fact the most famous prank was still to come, when in 1958 UCLA students rented a helicopter and dumped 500 pounds of manure onto Tommy Trojan. When USC students tell this story, the helicopter blades blew most of the manure back onto those sitting in the helicopter. The fact that UCLA students went to the extreme of renting a helicopter to get around the 24 guard of Tommy Trojan shows just how far things continued to escalate after the Victory Bell Agreement.
Was Traveler always the USC mascot?
USC has been known as the Trojans since 1912 for their fighting spirit in games against better equipped Cal and Stanford. The life size statue of Tommy Trojan on campus was erected in 1930 for the university's 50th anniversary. However, Tommy Trojan hasn't always ridden a white horse.
Back in the 1940s, live mascots were more common than the costumed mascots of today. Cal used live California Grizzly Bears until 1941, and UCLA had a series of bear Cubs until the 1960s. USC has a mascot who stood up to both of them, a little stray dog known as George Tirebiter. He was found chasing cars on Trousdale Parkway which bisects the USC campus. Adopted as team mascot, he used to lead the band onto the field for USC football games. He became famous for biting one of UCLA's Joe Bruin cubs on the nose. George was eventually run over by one of the cars he used to love to chase.
How long did UCLA and USC share the Coliseum?
USC started playing football games in the Coliseum in 1923, and UCLA moved in five years later in 1928. UCLA stayed in the Coliseum until 1981, so that's 53 years that the teams shared the LA landmark. With the advent of television, the series became known for the two teams both wearing their colors in the annual game between the two schools.