10 Oldest Characters In The Doctor Who Universe
4. Eldrad
Estimated Age: Over 150 million years.
As noted by the Fourth Doctor in 1976's The Hand Of Fear, members of the Kastrian race are "very difficult to kill", which means that they can live for a hell of a long time.
Eldrad is one such Kastrian, a silicon-based life-form that is encountered by the Doctor and Sarah Jane Smith in a 20th century English quarry. Eldrad has been here - or at least, part of Eldrad has been here - for 150 million years.
It's only Eldrad's hand that is discovered within the quarry, perfectly preserved inside a block of Jurassic limestone. However, because Eldrad is so powerful, he's able to possess Sarah Jane when she comes into contact with this hand, and this eventually leads to him regaining a full, humanoid form.
There's no telling how long Eldrad could end up living for, considering that, again, he's ridiculously hard to kill. Either way, surviving inside a hand for 150 million years is an impressive feat.