kot-begemot

const bip39 = require("bip39"); // mnemonic generator
const hdkey = require("hdkey"); // wallet lib
const ethUtil = require("ethereumjs-util"); // Used here for public address and public key generation

const mnemonic = bip39.generateMnemonic(); // generates string
const seed = bip39.mnemonicToSeedSync(mnemonic).toString('hex'); // creates seed for wallet

const root = hdkey.fromMasterSeed(seed);

const masterPrivateKey = root.privateKey.toString('hex');