10 Longest Gaps Between Doctor Who Character Appearances
7. The Zygons (13,945 Days)
The Zygons were David Tennant's favourite villain growing up, so it was a surprise that they never appeared during his tenure. Brilliantly designed, they were one of Doctor Who's most iconic one-shot monsters until they finally returned in 2013.
The inclusion of the Zygons in the 50th anniversary special The Day of the Doctor may have been an added sweetener to get Tennant back onboard, but recent developments suggest that the actor will take any opportunity to slip back into the role.
Between their first appearance in 1975 and their second appearance over 38 years later, the Zygons featured in comics, audio dramas, and novels, and were even mentioned in 2010's The Pandorica Opens - but were never actually seen. Their ability to shapeshift would've made them ideal foes for Aliens of London/World War Three, but for whatever reason, we got the Slitheen instead.
Thankfully, there was a much shorter gap between the Zygons' second appearance and their third, which came in 2015's The Zygon Invasion/The Zygon Inversion. They're still out there, among us, so hopefully we won't have to wait until Doctor Who's 90th anniversary in 2053 to see them again.