In Tom's birthday party, Tom is the __?__ of the party.

Guest of honor.

Is '[guest of honour](https://dictionary.cambridge.org/dictionary/english/guest-of-honour)' the MOST important person, or people, who are equally important, or does it cover important people in various degrees? Say Tom's principal, or the mayor, is at the party. OK they're just people but let's say they're important, but they of course aren't as important as Tom. Are they the guest of honour?

Is the Chinese word supposed to be 主角?

Maybe centre of attention? Man of honour? To fit into your sentence anyway

You could say focus but it would sound really off.

I'd say 'guest of honour' in that slot (British English) but delete the final 'of the party'. It's what seems to fit best. In the context, you can say 'guest of honour' regardless of whether Tom organised his own birthday party or someone else did it for him. 'life of the party' doesn't work here because it just means someone who is typically outgoing, extroverted and fun - it's just a personality description; there doesn't have to be a literal party happening at all! I'd also say 'At Tom's birthday party', not 'In Tom's birthday party'. (There are certain contexts where you might talk about being 'in' a party, but it's not so common. For instance, if you were at a party and went out for a smoke or just a breath of fresh air and were chatting to someone else out there, you might say to them, 'I'm off back into the party now' and it wouldn't sound odd. But that's more when you're referring to the literal physical space - you're about to enter the room where the party is being held.)

Hero of the day.

If it's his birthday that is being celebrated then we could call him "the birthday boy". I think North Americans can use the word "celebrant" but I'm not sure. If he is just someone attending the party he is a "party-goer" or "reveller". If he is the person who organised the party but is not the one celebrating the birthday then he is a "host".

Birthday Boy

In my mind, Tom would be the **subject** of the birthday party. Tom’s birthday would the *occasion* of the party, if you needed to know that as well. (FYI, the one whose birthday is being celebrated is generally assumed to be at their own birthday party; they don’t need to be “invited,” per se)

I'd say star but that's informal. Maybe focus?

Tom is the guest of honor.

Center

Both guest of honour and birthday boy work in New Zealand English, but it would depend on how formal the context is. Guest of honour is what I would hear used if it was a more formal event being hosted at a restaurant etc., whereas birthday boy is what I hear used if it’s a more casual house party. Also, if using guest of honour, we would usually say “at” rather than “of”, and if using birthday boy, we’d likely drop the “of the party” altogether

Star or birthday boy

Host?

Center of the party. Honoree of the party. Celebrant of the party.

Reason for the season

He’s the star of tonight would probably be how I would translate 他是今晚的主角.

To fit your sentence, I'd think you could use "focus".

others have already answered the question, so I'll just point out that it should be "At Tom's birthday party" rather than "In Tom's birthday party"

You could use the expression "star of the show".

Rather than "\_?\_ of the party" you could use "belle of the ball"

Life? As in , the 'life of the party' to mean, the one who makes it enjoyable or something. It depends if this tom person is fun but that's what I thought at first

If he's not the host, then he'd be the "guest of honor", "celebrated guest", or "celebrant" (the last one is really only used in North America, I think).

We would say "Tom is the **life** of the party" if he brings joy during the party. Otherwise, he would be the "guest-of-honor" or the "VIP" (very important person) of the party. If it's his birthday, he would be the "birthday boy."

Celebrant.

I like the phrase “Belle of the Ball.” It’s typically used for women but is fairly universal

if all you want to say is that Tom is prominently active in celebrating, then he can be the "life" of the party.

While I can understand people saying guest of honor, that sounds kind of stuffy to me or something only rich people would say at some fancy occasion. I think for more casual things, we say birthday boy, though it sounds a little playful.

Honoree, if you had to pick a word. I’ve never heard it used exactly like that though.

"honoree" (add the u for BE) is a simpler form of "guest of honor" that also works.

Tom is the guest of honor at his birthday party.

“Star” of the party

What about "Celebrant"?

Life of the party

Princess 👑❤️😘

Maybe "Tom's the star of the day"? It's not super native-sounding but if you say "Tom's the main character today" people will still get what you mean. There's the meme about avoiding becoming Twitter's main character where the nuance is very similar to 主役 in Japanese/主角 in Chinese: https://knowyourmeme.com/memes/twitters-main-character

Where I’m from people say “grilack of the grimfat” so that might work

\*AT\* Tom's party, he is the \*STAR OF THE SHOW\*.

Honoree

I feel like in a real life scenario you would normally just say, "It's Tom's birthday party," in order to communicate the role of Tom in relation to the party. He is not a guest, he may or may not be the host, but the party exists to celebrate Tom's birthday. If you had to phrase it as "Tom is the ____ of the party," you could say: "Tom is the focus of the party," "Tom is the head of the party" or even "Tom is the reason FOR the party" etc... Each variation conveys a slightly different meaning, but the most natural and straightforward way to communicate Tom's role is just "It's Tom's party."

Guest of honor or man of the hour would both work

The guest of honor is the person the party is for. This is distinct from the host, who arranged and/or provided a venue for the party. The other guests at the party have been invited specifically to celebrate the guest(s) of honor, and generally they are aware of this before arriving. For example, if we imagine that Tom is a pilot who managed to safely land a seriously malfunctioning plane, someone might throw a party to celebrate him. Tom isn't going to throw that party for himself; someone else will arrange it. That person will probably invite the passengers who survived thanks to his skill, Tom's friends and family, and so on. Those who attend will probably cheer and congratulate Tom when he arrives. By design, the evening will be about him. The life of the party is the person who makes the party fun. This isn't a formal thing; it's just something that happens. A person who is vibrant and engaging may be described as "the life of the party" after the fact. For example, if Tom is a college student, we can imagine him going to a frat party. He wasn't specifically invited, nor is the party meant for him in particular. He's as welcome as anyone else. However, over the course of the evening, he tells great jokes, does some cool tricks, and otherwise makes the party more fun for everyone around him. The next day, people refer to him as "the life of the party," and they're more likely to invite him to parties they plan in the future.

In the US, "life" is the only word that fits "the ____ of the party." No one here would say "the birthday boy of the party" or "the guest of honor of the party." You'd sound like you were repeating details in a way that no one does.

The only word I feel could fit in spoken english is: "At Tom's Birthday Party, Tom was the life of the party." But "the life of the party" is a way to describe someone who brings joy to those around them in a party setting, who's good mood is contagious and the party kind of follows their lead. Not necessarily the same as the "birthday boy" which would be a (slightly silly) common description that is more accurate about their "position" in the party. "It's Tom's Birthday Party." Is enough for most situations. It explains what the event is (a celebration of Tom's Birthday), and no one else could be the "target" or "subject" of the party. I guess if we were talking about a "retirement party" you might say the "retiree" of the party. But that is a very detached and clinical description that maybe a historian would use when describing the event without using any names: "During a retirement party, it became customary to burn the retiree's old uniform in a mock ritual." If you wanted a similar stand-in for a birthday party, you would use "birthday subject" I guess? "When celebrating the birthday of any family member, the birthday subject would be forced to drink one shot of vodka with each guest. This quickly spiralled out of control as the family grew larger and the number of guests outstripped the family member's drinking tolerance." But it would be rephrased to something like: "Tom was the subject of the party." I might be wrong, and there is a more precise word, but I don't think I've ever heard anyone use it! *(Edit: Guest of Honour! Someone else mentioned it. It's very formal, but "Tom is the party's Guest of Honour" makes perfect sense)*