A Federation agent, code-named Bartolomew. Anna was first mentioned in Countdown, when Avon met her brother Del Grant. Del had sworn to kill Avon, believing him responsible for Anna's death, but Avon managed to convince him that he had been unable to rescue her.
In Children of Auron Avon admitted that Anna had "meant a lot" to him, and that he planned to kill the man responsible for executing her. Rumours of Death supplied more details: Anna had been working with Avon on his fraud scheme - after he had been shot by the man supplying exit visas for himself and Anna, Avon had been forced to lie low for a while, only later finding out that Anna had been arrested and had died under interrogation.
In actuality, Anna had been assigned to monitor Avon, in the belief that his crimes were politically motivated. Anyone he came into contact with was brought in for questioning. Anna apparently staged her own death to conceal her secret identity: Del definitely believed that she was dead.
By the time of Rumours of Death Anna was married to Councillor Chesku and operating under the name of Sula. It is not revealed whether this was a formal change of name, a nickname or a whole new identity, but she was also known as Sula to the rebels she was working with. She expressed utter contempt for Servalan and her excesses, and also for Servalan's supporters such as Chesku, whom she shot dead. She did, however, persuade her own followers to keep Servalan alive to order Federation forces to stand down and hand over the reins of government. Sula's motives in attempting to overthrow Servalan were never clarified, nor exactly were those of her followers, although they at least seemed to be in favour of instituting a People's Council to replace the current regime.
Very few people knew that Anna Grant was Bartolomew. Chesku certainly did not, at least according to Servalan, and Del Grant appeared to have no idea. A "controller" from Central Security that Shrinker interrogated for the rebels did know, but died before he could reveal any details.
On meeting Avon in the cellar of Servalan's palace, Anna professed her love for Avon (whom she addressed as "Avon"), adding "I heard there was someone with Blake but I didn't know for sure". When questioned by Avon, she claimed to have run to "her husband" when Avon disappeared after being shot (although if genuinely married at the time she had retained her maiden name). This husband, she said, knew she didn't love him. Her dying words, after being shot by Avon, were: "I let you go, my love".
In flashback, Avon admitted that he trusted Anna, with the rider "I'm afraid I do", revealing the depth of feeling he had for her, and possibly (probably?) she for him. Many possibilities are hinted at in what various people said about Anna/Sula/Bartolomew, but very few real facts are to hand.