There are all sorts of different bots. A bot is just an algorithm - there are bots that target VWAP, TWAP, % of volume, and many others. These are execution algos they execute trades. Back in the day a human trader would sit there and break a $100m order into slices of $25k in order to try avoid pushing the price up (if you jam a $100m order onto most markets you'll probably break the market and a bunch of regulations at the same time). Turns out you don't need a human to do this - algo's ("bots") do it better. I have not seen market statistics but I believe these bots execute the vast majority on market trades based on their notional value (all the retail punters $2k trades pale in comparison to your super funds $1bn trade - you use your fingers they use execution algos / "bots")
https://blazeportfolio.com/blog/introduction-to-trade-execution-algorithms-2/Then there are the Quantative Hedge Funds - they have different types of "bots" which are statistically backtested trading strategies which (at least historically) should make money from trading. There are lots of different types of Quant funds and they often use statistical arbitrage or other similar techniques to give them buy/sell signals. Some of these funds only employ mathamaticians/scientists (no finance backgrounds - e.g. Renaissance Technologies). An overly simplified way to think about them is they look at data in real time, their "bots" will generate buy/sell signals and trade size and then pass those orders to the bots mentioned in the paragraph above for execution.
Honestly, there's probably all sorts of other examples - google and you will find them. I don't profess to know them all but I think I do have some value to add on the subject in this forum.
