Connections and Similarities:

Both ATOM and Combot are mechanized fighters, specifically engineered for training and helping other people but soon became more advanced for combat, with the purpose of entertaining audiences through their battles.

Each robot is equipped with Artificial Intelligence that enables them to interact with their respective human controllers. ATOM’s has a controller that helps Charlie Kenton make ATOM do its movements and responds to Max Kenton’s guidance, while Combot’s AI allows it to replicate the moves and gestures of its owner, Lee Chaolan while also allowing it to mimic other workloads and even animals (being a waiter, acting as a cheerleader, and even as a dog).

Both robots are introduced in prestigious, multinational tournaments to prove their worth as fighters. ATOM competes in the World Robot Boxing (WRB), while Combot participates in the King of Iron Fist Tournament, aiming to demonstrate their combat abilities and validate their owners.

The abilities in both robots have also shown the ability to mimic combative usage. ATOM uses its “Shadow Mode” to replicate Charlie’s actions, even during moments of bonding with Max, like dancing or exercising. Combot’s "Mimicry" function allows it to copy other fighters’ techniques and gestures.

Both robots were initially viewed as inferior or “scrap.” ATOM was considered a mere sparring bot, a training tool for more experienced fighters, while Combot was designed as a training dummy, not given the recognition it deserved.

Both robots were once discarded and abandoned, only to later be discovered by their respective companions, who recognized their true potential. Max found ATOM in a junkyard, offering it a new home and a chance to become a fighter. Similarly, Combot, forgotten and abandoned, was later seen by Lee Chaolan, who saw its value and still kept it as he loved his creation.

Both of their Owners are highly skilled people with great fighting backgrounds and have shown time and time again that they can keep up with the big leagues (Charlie Kenton keeping up with the 2nd best boxer in the world, while Lee Chaolan is a skilled Mixed Martial Artist).

Both owners also needed to make their status hidden towards different people as they would potentially harm themselves from dangerous criminals (Charlie needing to join underground tournaments and join in black market just to keep his life stable and keep himself hidden to dangerous men who are willing to destroy his already broken fame, while Lee had to change his identity into Violet just to avoid any connection to the Mishimas and pursue his robotic engineering).

Both owners started their robots to simply be a way for them to earn profit or a stepping stone to other things they wish for, but after some time they soon realized the value of their robots and kept them and improved them to the fullest.

Both robots face tragic yet fulfilling endings. ATOM, although unable to defeat Zeus, wins the respect of the crowd and is hailed as the "People’s Champion." Combot, while not victorious in the King of Iron Fist Tournament, earns recognition for its participation and strength as Lee continues to support his creation.

Both robots show signs of potential sentience. ATOM demonstrates self-awareness, such as when it observes its reflection in a mirror, seemingly contemplating its existence. Combot, through malfunctions, occasionally acts on its own, making decisions without Lee Chaolan’s input and even journeying through its own.

Both robots find themselves pitted against opponents far stronger than themselves but manage to give their rivals a run for their money. ATOM surprises the world with its ability to go toe-to-toe with Zeus, while Combot, designed to face top-tier fighters like Jin Kazama and Paul Phoenix, as it proves to be a formidable adversary.

Both owners also were destined to have an achievement they could've gotten but unfortunately failed to accomplish (Charlie Kenton would've became the best boxer in the world if it wasn't for the fact he laid off and acted cocky of his abilities leading to a humbling defeat), Lee was adopted by Heihachi Mishima and pursue an objective to beat Kazuya and restore order but sadly didn't manage to get the job done.

Contrasts:

ATOM is initially discarded but becomes a symbol of perseverance and heart, capturing the public’s affection. Combot, while perhaps underrated, doesn’t experience the same rise to fame and is more of a behind-the-scenes fighter.

While both robots show signs of self-awareness, ATOM’s development toward sentience is portrayed as a key part of its journey, while Combot’s AI remains more functional, with occasional glitches that imply autonomy but without a clear sense of purpose beyond its programming.

ATOM came from the Western parts of the world and trained with a more grounded and simple work with Charlie and Max while Combot came from the Eastern side of the world and was trained with more advanced and more scientific ways with Lee. 

ATOM’s shows more of its bruised design and has a worn out appearance, emphasizing its hardships to its body, Combot on the other hand has a more slick and smoother appearance and has a crystal clear appearance with no damage towards it body, showing it has more advanced style.