http://en.wikipedia.org/wiki/List_of...ass_characters
I doubt I can give better biographies than wikipedia(ha Nina's last name was Einstein, seriously?), but I can give my opinions of the characters that are still alive.
Lloyd Asplund - His interest in research seems to be above his interest in relations to others. Not only that but he appears to be in a technological arms race with Laksharta. He and Cecile have a previous relationship with Laksharta, but it is unclear under what terms it broke off. He is also responsible for the data that went in to designing Lelouch's Hadron Cannon on his Gawain, and the flying fortress which has become Lloyd's base of operations so to speak. As for the fans I'm sure we can expect some new inventions in the 2nd season from Lloyd.
Cecile Croomy - One of the few remaining important people to Suzaku. She apparently is replacing him for someone who we haven't learned about yet. I suspect her to be one of the only people other than Nunnaly capable of helping Suzaku get over Euphie.
Laksharta Chawla- The Research and Development chief for the Black Knights. We still are unclear what the past relationship was between her, Cecile, and Lloyd but I'm willing to be it ended badly even though Laksharta still has trust with Lloyd.
General Bartley - In charge of the original project with C.C. and most of the time a comedy aspect for the audience. Things just never seem to go Bartley's way except getting saved by Schneizel.
Gilbert Guilford- Guilford is an elite Knightmare pilot, is Cornelia's personal knight, commands troops well, and has become a rival for Todo Kyoshiro in the show. He has also become the commander for the Glaston Knights in the Battle for Tokyo.
Nina Einstein- Nina is also a character that has provided comedy to us throughout the 1st season, despite her level of intelligence. Nina has a very racist view towards the Japanese, and expresses it several times in the show. Honestly, I don't know where her character is going, I can only hope for someone to put a bullet in her head in the 2nd season so she stops taking screen time. She has vast knowledge of nuclear physics, and later uses it in the construction of her homemade bomb. Her Euphemia love crush caused a complete breakdown once Euphemia died and like many others seeks revenge against Zero.
Millay Ashford- She is the most calm out of the student council members, often keeping her cool even in times of crisis such as the hotel jacking and Ashford takeover. She is engaged to Lloyd, and is incredibly wealthy in many ways.
Rival Cardemone- friend to Lelouch and one of the earliest characters we meet. He is in fact responsible in a round about way for everything in the shows events starting from when he blocked Kallen's trailer with C.C. in it. He defends Millay and the other student council members when the OoBK take over the school. His crush on Millay, well we will just have to see how that works out in season 2.
Arthur- probably one of my favorite characters is this cat, thought I'm not sure if I like this cat because of his comedy aspect or because he bites Suzaku almost all the time or both.
Sayoko Shinozaki- I'm guessing she is supposed to be Nunnaly's bodyguard but seeing how much Nunnaly gets kidnapped. I'm surprised Lelouch hasn't fired her.
Shirley Fenette - Shirley has had an extremley tough time in this series so far from being kidnapped, to her father dying, to nearly killing her love, to getting geassed. Her character has become one of pity, and I don't see her romantic interest of Lelouch getting re-sparked.
Jeremiah Gottwald - Nickname: Orange-kun Even with his recent power up given by General Bartley Jeremiah has fallen from a high ranking officer to a lab rat experiment. The worst thing he has done was at the end of the most recent episode where one of our favorite characters C.C. is sinking his mech to the bottom of the ocean along with herself. Hopefully we can be rid of Orange-kun and move on to new villains in season 2.
Viletta Nu- A high ranking purist who has now regained her memory and will likely report to the higher Britannian officers in an attempt to gain nobility. Her biggest contribution to the war so far has been shooting the Black Knight commander Ougi Kaname.
Euphemia Li Britannia- She is the only dead character I am going to mention due to her importance. Her pacifistic ideals were enough to even sway Lelouch to join her before the massacre. She had many supporters and as a result of Lelouch killing her Lelouch has gained an unbelievable amount of enemies. Perhaps the most important of these being her relationship with her knight Kurugi Suzaku as he has caused the most problems for Lelouch. Euphemia was kind to a fault even risking her own life several times. Her death was not only the most tragic, but the most important in relation to the story because it has created a dividing line between Suzaku and his long time friend Lelouch; one that can only be broken by one of them or both of them dying.
Cornelia- Older sister to Lelouch, Nunnaly, and Euphemia. Another person who was shattered by the death of Euphemia. We have known about how closely Cornelia thought of Euphie, and she also values the lives of her army. Her view on numbers though is very different and will not hesitate to kill many numbers if it completes her objective. I suspect she is still alive.
Schneizel El Britannia- He is very intelligent as it is mentioned not only about his chess matches with Lelouch, but several plans including when Zero and Lancelot teamed up and using Euphie's S.A.Z. to stop resistance in Area 11. However, I only have Scheizel as #3 on Lelouch's list of main enemies. Hopefully Scheinzel won't be able to hold the Chinese Union and the OoBK can get some back up. He is one of Lelouch's suspects to be behind the murder of Lelouch's mother.
V.V. - I have V.V. tied with #2 with Suzaku as main enemies for Lelouch. V.V. is skilled, loves confrontation, and is bored three things that have created disaster for Lelouch. V.V. has the ability to teleport people, the limits of this ability we do not know. He put Suzaku close to Kallen, and Lelouch close to Euphemia the first time clearly trying to spark violence. All V.V. had to do was kidnap Nunnaly the second time and everything that Lelouch has worked for begins to crumble. Needless to say I don't think Lelouch and V.V. will be able to discuss their differences over a cup of tea.
Emperor or Britannia- this guy in addition to be a world class jackass, is also a major pimp. He has more wives then James Bond has women. The Emperor throws Nunnaly and Lelouch away to Japan then declares war on Japan. Honestly, I think to either kill Lelouch or have him grow up in a war area. Either way this is Lelouch's main villain / final boss so to speak. But if Lelouch is going to face the Emperor he is going to need Japan. He is also one of Lelouch's suspects to be the killer of his mother.
Ougi Kaname- A one time teacher and friend to Kallen's brother Naoto has become a commander with Lelouch's Black Knight army. He has recently been shot and even though shot ordered Kallen to retrieve Zero to help turn the tide back for Japan.
Kallen Kozuki/Stadfeld- It's getting harder and harder to choose between Kallen and C.C. as my favorite character. She has been Lelouch's most impressive Knightmare pilot and soldier. She has been fighting alongside Lelouch as Zero since the beginning in the Shinjuku ghetto but has only recently learned along with Suzaku that Zero is Lelouch. She proudly fights to avenge her brother's death, and change the world for her mother to live in an liberated Japan. However, at the revelation that her idol Zero is Lelouch her emotions are torn and she may have even shot and injured Lelouch(god i hope not) Kallen is a possible love for Lelouch.
C.C.- C.C. is many people's favorite character, and the one people want to know the most about. She gave Lelouch his Geass ability and has many herself included high speed regeneration even if shot in the head, or stabbed, or tortured, or set on fire.......Even though she often refers to herself as a witch, I haven't seen her do too many evil things except tease Lelouch and abandon Mao. She has lived for an unnamed amount of time at least a few hundred years. She has a scar which apparently cannot heal and for some reason needs Lelouch alive. Whether for her own purposes or because she genuinely cares for Lelouch or both is still uncertain but probably both. She has fought hard for Lelouch, and is more than likely in love with him. C.C. is a possible love for Lelouch also.
Nunnaly vi Britannia - She is Lelouch's cause and was Euphemia's cause. She has been through an incredible ordeal having her mother die on top her causing trauma and being paralyzed from bullets. Her kindness is the only person that reaches above Euphemia's. She was recently kidnapped again, and her condition is uncertain. Lelouch's devotion to his younger sister and wanting to create a peaceful world for her is something I admire as I also have a younger sister.
Kurugi Suzaku- The second main character behind Lelouch. He is Lelouch's first friend and his ultimate enemy. Where as Lelouch has gone against Britannia and is Britannian to create a peaceful world for Nunnaly and find his mother's killer. Suzaku has joined Britannia against Japan and is Japanese trying to change Britannia from within and is often called a traitor. Suzaku was on his way to completing this goal with Euphemia's S.A.Z. area pressing for equality. However, as soon as Euphemia shot that Japanese man in the front row, Suzaku's goals were killed also. Many morality debates have waged on this but I must keep my opinions about Suzaku out of this thread. Suzaku became the pilot to prevent people from dying but was really trying to die himself and repentance for killing his father. His position in the Britannian army has put him against Lelouch since the beginning of the season and will likely continue in the second season. Suzaku's physical abilities allow him to dodge bullets and pilot Lancelot at incredible speeds.
Lelouch vi Britannia- The main character of the series. Lelouch was born a prince and at the age of 17 has gained a superhuman ability, created a revolutionary army winning several battles against a superior power in Britannia, become the hope of Japan disguised under the title Zero, is extremely intelligent, and done all of this for the sake of his sister and to discover his mother's murderer. He has also done several evil things including killing innocent people in the Narita area, and assassinating two political leaders. Lelouch's identity was recently exposed to Cornelia, Suzaku, and Kallen but Cornelia was geassed and can only remember Kamenija being mentioned.
Wow, that was alot of typing and my hands are tired. Hopefully this will help you understand the characters more.