Pel had an uncle named Shmullus, who used to make her laugh. Pel later contracted the Phage at age seven and began receiving replacement tissue at that time. At some point she required use of a Cortical stimulator to compensate for some of her damaged brain tissue.
While returning from Fina Prime in 2372, where she was helping to treat an outbreak of the phage, she began suffering effects associated with the advanced stages of the disease, leading to a degradation of her neural patterns when the brain tissue linked to her cortical stimulator began to break down. She sent out a distress call, which was responded to by the USS Voyager. She was promptly beamed aboard.
In an attempt to save Pel's life, The Doctor put her body into stasis and used the cortical stimulator to transfer her brain patterns into a holographic body based on her own to prevent the collapse of her mind, giving him time to come up with an alternative treatment while also collaborating with her to acquire more detailed information about the disease. Taking advantage of the time this allowed him, The Doctor convinced B'Elanna Torres to donate some of her Klingon tissue, previously proven at least partially resistant to the Phage, to be grafted onto Pel's brain and hopefully cure the damage the disease had caused to her brain.
While Pel and The Doctor waited to see if the procedure worked, they developed feelings for each other, Pel appreciating the Doctor's sense of humour and compassion while the Doctor admired her medical abilities and willingness to be open with him; Pel even took to calling The Doctor 'Shmullus', after her favourite uncle, one of the few names he used more than once. Initially, Pel was reluctant to begin a relationship, unused to compliments due to her generally repulsive appearance, and rejected The Doctor's initial advances, but after Pel had talked with Kes and The Doctor had taken relationship advice from Tom Paris, the two of them gave it another shot and began a relationship.
The procedure to cure Pel's damaged brain tissue proved a success, but she was reluctant to return to her ravaged body and she tried to sabotage the procedure. Ultimately The Doctor did convince her to return to her body and continue her work in finding a cure for the Phage, subsequently sharing a dance with her on the holodeck in Sandrine's in her real body before she had to depart. (VOY: "Lifesigns")
Later that year, The Doctor contacted her for information on a poisonous insect that had infected Captain Janeway and Commander Chakotay. She managed to get the cure to him, even though her superiors tried to attack Voyager, calling him 'Shmullus' once more before they parted ways for good as Voyager fled the attack. (VOY: "Resolutions")
Denara Pel was played by actress Susan Diol. Dr. Pel is the only healthy Vidiian (albeit in holographic form) to have appeared in any Star Trek series or movies.
It may be inferred that The Doctor and Denara may have had sexual relations during their relationship based on dialog in "Message in a Bottle" where The Doctor, while talking with the EMH Mark II, mentions that he has engaged in sexual activity. Denara is perhaps the only woman who was shown to have been involved with The Doctor in that sense. It is also possible that The Doctor may have done so with his wife, Charlene, from his holo-family seen in "Real Life".