Sergeant Benton was a regular character in the Third Doctor era, and appeared in the early episodes with the Fourth Doctor. His first name was never stated in the series, but a variety of other media used the name 'John'. He was one of UNIT's faithful, extremely loyal, and often willing to go against orders to help his friends, particularly the Doctor. His most famous quote is from 'The Three Doctors', from the first time he went inside the TARDIS:

Doctor: Well Sergeant? Aren't you going to say it's bigger on the inside than it is on the outside? Everybody else does.

Benton: Well, it's pretty obvious, isn't it?

Sergeant Jonathon Robert Benton of UNIT

"Uh, Mr Benton, John…"

"Call me Benton."

Jonathon Benton. On the face of it, there was nothing wrong with the name. John was a good, serviceable name. Anyone could respect a man named John.

Except his name had come from his father, the father he'd never met.

Now, Benton… that had come from his step-father, the man his mother had married when he was just a baby, the man who brought him up. John was the name of the man who left; Benton was the one who stayed behind.

When he was just a nipper, people had called him Bobby, from his middle name, but that was too childish to carry with him to the army. So he introduced himself as Benton. John went on the army, and eventually the UNIT records, but barely anybody knew that was his name.

In the army, he had flourished. He had been promoted quickly through the ranks: Private Benton, Corporal Benton, Sergeant Benton… he had been Sergeant Benton for a long time. When he was promoted again, he had been a bit sad to lose the title. Warrant Officer Benton didn't have quite the same ring to it.

But the name John had clung to him like a shadow, and in a time where it was no longer proper to use last names in familiar company…

He had idly considered changing his name, but what would be the point? Even if he did become, for example, Samuel Benton, would that change anything? He would know in his heart that he was really John, and it would continue to haunt him.

But overall, he was, forever Benton.