T'Pol was a Vulcan who served aboard Enterprise NX-01 in the mid-22nd century. She was the first Vulcan to serve aboard a Human ship for any substantial period – Enterprise was a prequel so T’Pol predated Spock.
After an assignment in the Vulcan Embassy on Earth she was temporarily reassigned to the Earth Starfleet vessel Enterprise with the rank of Subcommander. At the conclusion of the missioon T’Pol was persuaded by Archer to remain aboard taking the position of science officer and the title of first officer of Enterprise and was later promoted to the rank of Commander. T’Pol joined Captain Archer on Earth for the founding ceremony of the United Federation of Planets.
On the Enterprised she formed a relationship with Commander Tucker but it was problematic and eventually didn’t work out.
In an alternative timeline in the episode ‘E²’ Enterprise was trapped back in 2037 and an aged T’Pol met her younger self when the two versions of the Enterprise rendezvoused in 2154.
Michael Westmore was the makeup designer and supervisor.
In the third season there was a major change to TPols appearance in both her makeup and her costume: she got a sexier uniform, a better looking wig, Vulcan eyebrows, and lipstick. There have been various explanations for the changes.
On Memory Alpha I have seen an article stating that: ‘Jolene was a Trek fan and she hated that they didn’t give her usual Vulcan ears and eyebrows. So in season 3, she and her makeup artist just went ahead and made the change. When she appeared on the set with her new look, no objections were raised.’
For myself, I am more inclined to accept Bob Blackman’s explanation: ‘The ratings dropped. That’s the frank, real answer. … There wasn’t enough raw sex appeal.’