Tashek was the elder sister of Colonel Nasgard, a senior member of the Kaled Military Elite, and the aunt of Yarvell and Davros. She lived on Skaro towards the end of the Thousand Year War between the Kaleds and the Thals. She helped her sister-in-law Lady Calcula raise her children while she was away from home serving in the House of Congress. Her ancestors in the House of Nasgard had owned a home beside Drammankin Lake for several centuries.
A former nurse, Tashek knew from her brother's medical records that he was sterile and therefore not Davros's biological father. However, she seemingly did not know that Councillor Quested was Davros' father. Calcula hated Tashek for knowing the truth and Tashek hated Calcula for not telling Nasgard the truth and for favouring Davros over Yarvell. Shortly after Nasgard returned home due to his deteriorating health, Tashek told him that he was not Davros' father. Minutes later, they were both killed by a bomb planted by Calcula. (AUDIO: Innocence)