18 July 1926: birth of Robert Sloman, who co-wrote The Dæmons (1971), and was sole author of The Time Monster (1972), The Green Death (1973), and Planet of the Spiders (1974) - the season finales for all but the first of the Pertwee years.
18 July 1930: birth of Alan Bennion, who appeared as Ice Lord Slaar in The Seeds of Death (Second Doctor, 1969), Ice Lord Izlyr in The Curse of Peladon (Third Doctor, 1972) and Ice Lord Azaxyr in The Monster of Peladon (Third Doctor, 1974).
18 July 1967: birth of Paul Cornell, who wrote televised stories Father's Day (2005) and Human Nature / The Family of Blood (2007), the latter based on one of his eight Who novels, and the webcast alternative Ninth Doctor story The Scream of the Shalka (2003), as well as four-and-a-bit Big Finish audios, contributing to The Discontinuity Guide, and editing one of the Short Trips anthologies. I took the picture below at Gallifrey One last February, with fellow writers Matt Fitton, L.M.. Myles and Una McCormack. If you're reading this, happy birthday, Paul!
18 July 2006: death of David Maloney, who was one of the great directors of the classic series: The Mind Robber (1968), The Krotons (1968-69), The War Games (1969), Frontier in Space (1963), Planet of the Daleks (1963), Genesis of the Daleks (1975), Planet of Evil (1975), The Deadly Assassin (1976), and The Talons of Weng-Chiang (1977) all benefited from his talents.
ii) broadcast and production anniversaries
18 July 1964: broadcast of 'A Race Against Death', the fourth episode of what we now call The Sensorites. The Doctor is trying to save Ian, and tracks down the poison in the city's water supply to its source. But something 'orrible lurks in the tunnels...
18 July 2004: the very first filming of New Who, the scene in Aliens of London (Ninth Doctor, 2005) with the Doctor, the pig and Toshiko Sato.
iii) dates specified in-universe
18 July 2004: Setting of the first half of the rather good 2003 Sixth Doctor/Seventh Doctor crossover audio Project: Lazarus.
18 July 1699: Date of the final scenes of the 1998 First Doctor novel The Witch Hunters, most of which is set a few years earlier during the Salem witch trials.