Del Grant was a mercenary, responsible for a revolution on Arcos and called in by Cauder on Albian to overthrow the Federation's control of the planet. The garrison was defeated under his command of the rebels, but not before the solium radiation device was activated by Tronos. When Blake arrived, Grant recognised Avon instantly. Avon believed until then that Grant was dead (Grant also believed that Avon had himself died). Having some knowledge of timing devices, he worked with Avon to disarm the solium device.
Del was Anna Grant's brother, and believed not only that she was dead but also that Avon was, albeit indirectly, responsible, having left with the exit visas before he knew Anna was dead. He appeared to have a very anti-Federation attitude, and was thus perhaps not completely mercenary. He did demand a high fee for his services, but apparently because his reputation (and ego) demanded it. (B: Countdown)
He later contacted Avon when he was contracted to deal with a super weapon. He went with Avon to the prison complex where the scientist behind the weapon was kept. He learnt about how the weapon came into being. Grant and Avon learnt what the superweapon was and that it was the prison commandant that had contacted Grant. He wanted to destroy the ships that contained the weapon after the weapon was deployed. Avon and Grant went to the planet's surface to find his fellow crewmembers. He became angry when he thought that he was Avon was running a fools errand. He arrived to stop Avon from being killed. During this, Grant learnt from Avon that Anna had turned out to be a Federation agent. Although initially angry with Avon for killing Anna, Grant later admitted that he had always feared that his sister would pick the wrong side. (AUDIO: The Armageddon Storm) Grant ultimately blamed the Federation President for corrupting Anna and causing the circumstances that led to her death. (AUDIO: Devil's Advocate)
He stayed as a member of the Liberator Crew. He showed the crew about a rebel who had defected, Avon sent him and Tarrant to find the defector and kill her. They pretended to be delegates of a conference to get into close to the federation. They encountered Servalan before heading to the conference room where they waited to perform the deed. Their plan was intercepted as an apparent failed assassination attempt on Servalan, however it was actually a cover for a defected federation officer, and the original rebellion had died to cover this. (AUDIO: Defector) He went with Vila Restal and Solvin Tavac to get the list of rebellion spies from a black market auction. He knew of the person selling the file and agreed to attend the auction for it. He had to convince Avon that this was a good thing to do. (AUDIO: Secrets)