Who appeared in most Dr episodes?

That's a tricky question! It depends on what you mean by "Dr." and what counts as an episode.

If you're talking about the Doctor Who series:

* Tom Baker played the Doctor the longest, appearing in 172 episodes from 1974 to 1981.

* William Hartnell played the Doctor in 134 episodes from 1963 to 1966.

* Patrick Troughton played the Doctor in 120 episodes from 1966 to 1969.

However, if you consider spin-offs and audio dramas:

* Peter Davison has appeared in a huge number of Big Finish audio dramas as the Fifth Doctor, making him a strong contender for most appearances overall.

It's also worth noting that David Tennant has appeared in the most episodes as the Tenth Doctor (since the revival in 2005), with 134 episodes.

So, the answer really depends on what you're looking for!