Fukuzawa is a tall man who always has a stern expression over his face. He has long silver hair, which ends just above his shoulder. He has metallic blue eyes, which also appear to have wrinkles/slight eyebags under them.
He is always seen wearing a green yukata under a black haori (a traditional Japanese thigh-length kimono-style jacket, commonly worn by men) with golden borders with a zigzag pattern, and zori (flat sandals) with white tabi (toe-divided socks).
Twelve years ago, before the Agency was founded and Fukuzawa was still under Sōseki Natsume's tutelage, he wore a black hakama (a pair of large, pleated, traditional trousers), a kimono underneath a longer haori and a small scarf with a circle pattern on it. His hair was also shorter.
Fukuzawa is (as expected from the director of the Company) a serious man, capable of maintaining his calm expression at every time, even in front of an enemy. He is also a good leader.
It is revealed as well that he possesses a caring side, as seen when he orders all the personnel from the agency to focus on finding and rescuing Atsushi. Therefore, he seems to care about his subordinates a lot, and he completely trusts in them.
However, his caring side does not minimize his undisputed authority over all Agency members: a frightened Edogawa Ranpo drops the idea of finding a nice, interesting murder case to solve instead of saving Atsushi after Kenji warns him against Fukuzawa's wrath if he does so. While Fukuzawa is emotionally reserved and impassive, he can display a scathing sense of humor: twelve years ago, while he was on his way to save Mori from low-level criminals, the criminals threatened to kill the doctor and Fukuzawa wished them to have fun doing so.  He's never seen smiling, although it's heavily implied he has a soft spot for cute things. After Kyōka makes a cute face, he hires her on the spot.  It's also been shown that he loves cats to the point where he keeps treats for them in the sleeves of his yukata. 
His ability, All Men Are Equal (人上人不造, Hito no Ue ni Hito o Tsukurazu?), allows him to suppress the abilities of those in the Armed Detective Agency. According to Dazai, it can “adjust the power of their abilities so that they may be controlled.” However, applicants have to pass an "exam entrance" (i.e. they have to display values compatible with the Agency's in perilous situations) to fall under the range of the ability.
Fukuzawa's swordsmanship and proficiency in martial arts are both unmatched. He possesses enough strength and reflexes to take on a group of assassins. It is also mentioned that he is Kunikida's master and has never lost a match against him.
When Fukuzawa was young, he trained at a government-run school of martial arts. He was good friends with Fukuchi while in martial arts training. They had a friendly rivalry and spent time together after Fukuzawa took in Ranpo as well. Fukuzawa was a part of the Goken, the five greatest swordsmen in the government. He worked as an assassin who was tasked to kill war hawk bureaucrats and the leaders of foreign military parties who supported them towards the end of the Great War and earned himself the nickname of Silver Wolf as his skills were unanimously praised. He stepped down from this position after he realized that he was starting to look forward to killing his targets because of how simple and easy assassinations were to him. He was shunned for this decision, but he ultimately permanently laid down his sword and became a 'lone wolf'. 
Twelve years before the Agency was founded, Fukuzawa was a notable martial artist who was working as a bodyguard. When his client (a company president) was murdered, he met Ranpo, who happened to be at the scene of the crime for a job interview. Ranpo easily pointed out who the murderer was, and thus Fukuzawa owed him a favor to help him find another job. Not wanting to get involved with Ranpo but also not wanting to leave him alone, Fukuzawa made up the lie that he was an ability user so Ranpo's view of the world would not collapse and wouldn't be scared of people not understanding him.
Later, when Ranpo tried to track down a criminal by himself and got kidnapped, and Fukuzawa realized how dangerous it was to leave Ranpo on his own and went to save him (and scolded him soon after). Fearing that Ranpo would become the target of corrupt organizations, he became determined to create a safe place for Ranpo to use his skill. Thus, the Armed Detective Agency was founded a year later, with the intent of being an organization for ability users to protect the weak and fight for justice, and Fukuzawa definitively put an end to his career as a bodyguard.
When celebrating the opening of the Detective Agency, Fukuzawa invited Fukuchi and introduced him to Ranpo. After Fukuchi kicked up a fuss because he had arrived already drunk, Fukuzawa defended him to Ranpo, calling him his childhood friend and the most reliable person in the world. He suspects that Fukuchi might be lonely, because he had found his 'life path' first. 
Around the same time, as Fukuzawa was still planning to establish the aforesaid agency, Natsume asked him to protect Mori, then an underground doctor. Since then, the two men have fought side by side and against each other several times.
Battles and Events
The Guild Arc
- Yukichi Fukuzawa vs Port Mafia underlings: victory
- Yukichi Fukuzawa vs Ōgai Mori: unsettled
- Yukichi Fukuzawa vs All Men Are Equal: draw
- Yukichi Fukuzawa vs Vita Sexualis: victory
- Yukichi Fukuzawa vs Nathaniel Hawthorne: defeat
- Yukichi Fukuzawa vs an unnamed group of criminals (twelve years ago): victory
- Yukichi Fukuzawa and Ōgai Mori vs an unnamed group of criminals (twelve years ago): victory
- Yukichi Fukuzawa vs Ōgai Mori and Elise: defeat (saved from death by Natsume's intervention)
- Yukichi Fukuzawa and Ōgai Mori vs Alexander Pushkin: victory
The Decay of Angels/Hunting Dogs Arc
- Yukichi Fukuzawa vs Ōchi Fukuchi: unsettled
- (to Ranpo Edogawa) "A comrade is in danger. We need to rescue him. Is there some weightier logic in the world which trumps that?" 
- (to Francis Scott Key Fitzgerald) "A human life is priceless, and,in its own way, so is that license. That is the soul of our company. It contains the very heart and soul of Natsume-sensei who devoted his all to bringing that agency to our side. You noveau riche types, heads stuffed with bales of cash... you could never obtain one that easily." 
- (to Port Mafia assassins) "Go back to your master and tell him, "good try". Continue to target me and me alone. If you do anything to my subordinates, I will snap your necks, no matter what it takes."
- (to his people) "Only one of the three organizations can survive. Our only course of action is to fight!"
- (to Ōgai Mori) "And you still haven't grown past your habit of killing people with a scalpel, Doctor Mori. Are you still attracted to little girls?"
- (to Ōgai Mori) "Because that's our sole similarity: that we love this city. As people of this city, as organizations that work to protect it, we cannot allow foreign gifted to raze it."
- (to his people) "You mustn't fight with the mafia... you must protect the balance and peace of the city over my life!"
- (to Ōgai Mori) "You have the same disgusting stench like me."
- (to Armed Detective Agency members) "To us, praise and rewards are a light drizzle. Even if we were underground thieves with no honor, we must stake our lives to prevent this murder. " 
- Kunikida and Fukuzawa also share a teacher/student relationship, as Kunikida is quite proficient in martial arts thanks to the President's teaching. 
- Fukuzawa entrusts Kunikida with the task to lead the Agency should the need arise or when the day of Fukuzawa's death comes. His choice is upheld when Kunikida has to act as interim president since Fukuzawa is down during the Cannibalism arc.
- Ranpo seems to care greatly about Fukuzawa, who gave him a place to belong to, as implied when the young man did not leave Fukuzawa's bedside during the early Cannibalism events. Although Fukuzawa is emotionally more reserved, the feeling seems to be fully reciprocated.
- Fukuzawa and Mori were affiliated with each other in the past before either of them became the leaders of their respective organizations. They fought together on several occasions, and both were under the tutelage of Sōseki Natsume and were trained to maintain a balance of power that would protect Yokohama, as part of the Tripartite Tactic.
- Fukuzawa's nickname, Silver Wolf, finds its origin back to the time when he always worked alone as a bodyguard, hence acting like a "lone wolf"; it is also a nod to his hair color.
- Much like his real-life counterpart, Fukuzawa is almost never seen wearing Western-style clothes, preferring traditional Japanese ones; the exception being during the awarding ceremony at the beginning of the Decay of Angels/Hunting Dogs arc. 
- Fukuzawa has never been seen smiling in the manga until chapter 80 . He is, however, in the anime, at the end of the Cannibalism events after he congratulated his subordinates for their work.
- During the Decay of Angels Arc, it is revealed that Fukuzawa is not married. Ōchi Fukuchi reminds Fukuzawa about a countryside woman named Kin while the President is in custody; it is implied that she and Fukuzawa knew each other in a way or another a long time ago. The woman is a direct reference to real-life Fukuzawa's wife, Okin. 
- He shares his birthday with Kōyō Ozaki, on 10 January.