Dash Rendar is a character that only existed in the Expanded Universe. He never made an appearance in a movie and most of his time came in the novel Shadows of the Empire and a game by the same name.
Expanded Universe: Dash Rendar pursued a career in the Imperial Navy instead of joining the shipping business that his family had established. When his family ran into trouble with Prince Xizor of the Black Sun crime syndicate, by not selling their business, Xizor had a freighter sabotaged and killed Dash’s older brother when his ship crashed into the Imperial Museum. The Emporer blamed Dash’s family and exiled them from the Core Worlds and kicked Dash out of the Imperial academy.
In the Outer Rim, Dash earned himself a reputation as a smuggler. He picked up his own ship, the Outrider, and led a successful smuggling business. Dash and his crew agreed to protect Holostar Javul Charn during her tour. She had initially told them that she needed protection from an overzealous fan but after surviving multiple attempts on her life, Dash had to figure out the truth. They found out that Charn was actually a member of the Rebel Alliance and Imperial Security and part of Black Sun were trying to kill her. Dash was able to get Charn to Alderaan, but he failed to see any reason to join the Rebel Alliance, though he occasionally went to work for the Rebels if the pay was good.
One of these times was a delivery to Echo Base on Hoth just before the Empire attacked. Han, a friend of Dash’s, convinced Luke to let him fly with Rogue Squadron to help cover the escape of the transports during the Battle of Hoth. Dash was credited with a kill on an AT-AT. Dash was able to escape and rejoined the Rebels.
Dash was with the Rebels whenever he found out what the Empire had done to Han Solo. He had learned that Leia was willing to pay well for locating Fett and rescuing Han that he agreed to take the job on as a favor for Lando.
Rendar tracked Fett to Ord Mantell and ended up in a firefight with Fett and an assassin droid named IG-88D. Rendar was able to defeat the droid, but Fett had gotten away. Rendar reported to Calrissian that they were headed to the moon base on Gall. Dash traveled to Gall and ended up in another firefight with Fett with Fett trying to leave the planet. During his departure, Dash was able damage Fett’s ship enough that he had to stay on the base while Dash left and reported his position.
Leia, Lando, Chewbacca, and Luke all showed up with Rogue Squadron to try and free Han. Dash led them on an attack run on the base, but pulled out before any actual fighting began. Meeting back up with the Rebels at their makeshift base, they were angry at Dash for abandoning them. Dash pointed out that he was only paid to lead them to Fett’s location.
Dash was paid by Leia to watch over Luke as he returned to Tatooine to await Fett. After an attempt on Luke’s life, Dash makes his presence known and a messenger droid shows up, asking Leia to meet with some people on Bothawui, the Bothan homeworld. Dash and Luke go in Leia’s place. Dash and Luke were introduced to a squadron of Bothan pilots whom had found out about a secret Imperial project and were going to steal the location. During the fight, Dash failed to stop a missile that was coming at the Bothan squad and it ended up destroying four Y-Wings. They were able to board the freighter and steal the information, which would end up to be the location of the second Death Star.
After this, Dash and Luke had to rescue Leia from Prince Xizor on Coruscant. Moving in through the sewage tunnels they were able to break into the palace and grab Leia. Xizor retreated to his skyhook. Vader had found out that Xizor was behind the attempts on Skywalker’s life and destroyed the skyhook, allowing Dash and his company to escape.
Now remember, this information is all Expanded Universe and is not canon.