Lance is not a rare name, but its rare enough that if you say Lance in the context of Complexity Theory, people know who you mean. Bill (or William) is a common name. There are two in my department: Bill Arbaugh who does security and Bill Pugh who does PL (he is known to the theory community for inventing skip lists). They don't do theory, but Bill Rounds, Bill Steiger, , Bill Roscoe, Bill Hesse, Bill Harrison all do. I don't know who Bill Marion is, but he wrote an article about why Discrete Math is good for computer scientists to know (the topic of another blog perhaps). (Some of these Bill's call themselves William.)
Which famous people are only known by one name? This depends on what you mean by famous and known. I could not find a list on the web, but by poking around I made up my own. Additions are welcome. I list them with comments on if I count them or not and why.
- Bono- Paul Hewson. YES- Never knew his first name. Or his last name. Music.
- Charo- Maria Rosaria Pilar Martinez Molina Baeza. YES. I can see why she went to one name. Actress?
- Cher- Cherilyn Sarkisian LaPierre. YES. One name is better than her real name. Music and Movies.
- Edge- David Evans. NO- never heard of this guy. Music.
- Elvira- Cassandra Peterson. YES- A C-list celeb or lower. Could have used her real first name. Actress?
- Elvis- Elvis Prestly. YES, though his last name is well known. Music.
- Elvis- Elvis Costello. NO. He should have used Costello. Music.
- Halston- Roy Halston Frowick. NO- never heard of this one. Fashion Designer.
- Hammer- Stanley Kirk Hacker Burell. YES- though I thought he went by M.C. Hammer. Music.
- Kreskin- George Joseph Kresge. Jr. YES- he was a famous mindreader.
- Liberace- Wladziu Valention Liberace. YES. Didn't now Liberace was really his last name.
- Madonna- Madonna Louise Veronica Ciccone. YES. Didn't know Madonna her really her first name. Music.
- Prince- Prince Roger Nelson. YES. Didn't know Prince was really his first name. Also used this as a name. Music.
- Sting- Gordon Matthew Sumner. YES. Could have used Gordon or Sumner as his one name. Well... maybe not. Music.
- Mr. T- Lawrence Tureaud. YES- Is this one name? I say YES. Actor?
- Topol- Chaim Topol. YES. Actor.
- Twiggy- Leslie Horby. YES- Was more famous in an earlier era, but still a celeb. Dancer.
- ***SORELLE***- a grad student in my department. She will be famous one day. She already has the name for it.