It has to be difficult being immortal. As Ashildr explained during ‘The Woman Who Lived,’ there are a unique set of problems that an immortal has to face. After all, everything they know and love eventually comes to an end as they continue forth, a fate that the Doctor has come to learn with his own adventures on Doctor Who, given his typically human companions.

However, it must certainly help Ashildr to know that she is not the only immortal. While she did figure out a career path in regards to watching over those who the Doctor has to leave behind, there are other immortals out there. Or, if Sam Swift truly turns out not to be, then there may only be the one – Captain Jack Harkness.

While it turned out that Ashildr had not heard of him yet, which makes sense since Captain Jack does not originally appear until about 300 years later, it was interesting that he was mentioned during ‘The Woman Who Lived.’ With the way that the Doctor mentioned him, and the expectation that Ashildr and Captain Jack would cross paths at some point, it seems to be a unique bit of foreshadowing.

With Doctor Who paying different homages to the past with the Twelfth Doctor, and the return of River Song this season, it may not be outside the realm of possibility that Captain Jack could return. The show has brought back several fan favorites, with River and Osgood coming back, so the return of one more would not be that surprising.

The return of Captain Jack would also make sense if Ashildr is being set up as a recurring character. Having her around to take care of those that the Doctor leaves behind, those who have been caught up in the tidal wave that he causes, would seemingly lend itself to such a role. With that being the case, having an ally like Captain Jack, one that would be able to survive along side of her and knows what it is like to travel with the Doctor, could be exactly what Ashildr needs.

Immortality, while it is certainly an intriguing thought and something that everyone has likely pondered in their lifetime, certainly does not appear to be for the faint of heart. Seeing all the pain and suffering, while watching everyone you know die, can certainly be difficult for anyone. Having someone that knows what it is like to go through that time and time again could certainly help.

Ashildr appears as though she could be a recurring character on Doctor Who. If so, hopefully this leads to the return of Captain Jack in more than name alone.