The Big Bang Theory

Leonard Hofstadter played by Johnny Galecki
Dr Leonard Hofstadter is an experimental physicist who also rooms with Dr Sheldon Cooper and really seems to be the nucleus of the 'geek hub'.

Sheldon Cooper played by Jim Parsons
Dr Sheldon Cooper is a theoretical physicist who is, in my opinion the star of the show, albeit an incredibly annoying person with OCD tendencies

Howard Wolowitz played by Simon Helburg
Mr Howard Wolowitz is a mere engineer who works with the other 'geeks' at the university and is often talked down to by Sheldon because of his lack of a doctorate!

Raj Koothrappali played by Kunal Nayyar
Dr Rajesh Koothrappali (Raj) is Howard's best friend and is an astrophysicist from India. He also suffers from Selective Mutism which leads to a lot of fun on the show.

Penny played by Kaley Cuoco
Penny's surname has yet to be mentioned on the show and she is Leonard and Sheldon's neighbor across the hall. A wannabe actress she presently works as a waitress at the Cheesecake Factory.

There are also some great supporting actors that appear in some episodes – Sheldon’s mother is played really well by Laurie Metcalfe while Leonard’s mother is played hilariously well by Christine Brananski.

Besides the original main five characters on the show the other notable cast members include -

• Stuart - Stuart is the owner of the comic book store where the four guys go every Wednesday as it's 'new comic book day' in the words of Sheldon.   It's also been claimed (on the Big Bang Wiki) that this is where Sheldon buys all of his shirts although I don't recall ever seeing him purchase apparel there.
• Leslie Winkle -  Leslie is a fellow physicist at the University in fact she has been referred to as a female Leonard.   She gets on well with all of the guys except Sheldon who she constantly winds up which he hates.   She refers to Penny as Barbie and has no time for here.
• Dr Eric Gablehauser - Dr Gablehauser is the head of the Physics department which makes him the boss something which Sheldon really doesn't appreciate.
• Mary Cooper - Played brilliantly by Laurie Metcalf, Mary Cooper is Sheldon's mother, a god fearing, church going Texan who says that Sheldon got his brains from Jesus.
• Beverley Hofstadter - Beverley Hofstadter is played by Chrisine Brananski and is Leonard's mother in a role that is completely unlike any I've seen her play before.   Sheldon is very envious of Leonard as Beverley (a neuroscientist and psychiatrist) is a very overy analytical person.
• Dr Koothrappali (Raj’s father)
• Mrs Koothrappali (Raj’s Mother)
• Barry Kripke - Barry Kripke also works at the University and him and Sheldon do not like each other, although Sheldon tries to become his friend in the episode - The Friendship Algorythim.
• Bernadette - Bernadette works with Penny at the Cheesecake Factory and is set up on a date with Howard.   The date goes horribly until they start discussing their respective mothers.   They are now engaged!
• Amy Farrah Fowler - Amy Farrah Fowler is like a female version of Sheldon and Howard and Raj found her online in an attempt to set Sheldon up on a date.   She's decided that she is now Penny's best friend and is now a main member of the cast along with Bernadette.
• Priya Kothrappali - Priya is Raj's sister who is also dating Leonard which has a whole new set of fun episodes.
• Stephanie Barnett - Stephanie is a doctor and dated Leonard for a while, something which Sheldon was really happy about and he set about trying to make sure Leonard didn't mess this relationship up.

Johnny Galecki
John Galecki's father was in the US Air Force which is why the actor was born in Belgium. He was cast in his first movie in 1989, but it's television that I know him from. He has had a role in Roseanne and now is one of the stars of CBS's hit show The Big Bang Theory.

Simon Helberg
Simon Helberg attended the famous NYU Tisch School of Arts and has numerous acting credits on his file, but I first noticed him when he was cast as Howard in The Big Bang Theory.

Kaley Cuoco
Kaley Cuoco has been acting and modeling since the age of 6 which makes her already a veteran even though she's still only in her 20s! She has starred in hit shows such as 8 Simple Rules and Charmed before being picked as the main female role in The Big Bang Theory.

Super heroes, comic books, video games and sci fi play a regular role on the show Big Bang Theory as the four guys are definitely what you would call geeks – the lovable geek, the ocd geek, the creepy geek and the shy geek.

Their geek style interests is even reflected in their wardrobes in particular Sheldon’s t-shirts and Howard’s belt buckles and then there’s the underwear, but we won’t go there!

Howard Wolowitz Belt Buckles
Howard is known for his collection of belt buckles from Batman to Pac Man you can rely on Howard to bring belt buckles back to the fore of the fashion world......unlike the rest of his wardrobe!